In the evening, after the contest Ilya was bored, and he really felt like maximizing. He remembered that he had a set of n sticks and an instrument. Each stick is characterized by its length li.

Ilya decided to make a rectangle from the sticks. And due to his whim, he decided to make rectangles in such a way that maximizes their total area. Each stick is used in making at most one rectangle, it is possible that some of sticks remain unused. Bending sticks is not allowed.

Sticks with lengths a1, a2, a3 and a4 can make a rectangle if the following properties are observed:

  * a1 ≤ a2 ≤ a3 ≤ a4
  * a1 = a2
  * a3 = a4



A rectangle can be made of sticks with lengths of, for example, 3 3 3 3 or 2 2 4 4. A rectangle cannot be made of, for example, sticks 5 5 5 7.

Ilya also has an instrument which can reduce the length of the sticks. The sticks are made of a special material, so the length of each stick can be reduced by at most one. For example, a stick with length 5 can either stay at this length or be transformed into a stick of length 4.

You have to answer the question — what maximum total area of the rectangles can Ilya get with a file if makes rectangles from the available sticks?

Input

The first line of the input contains a positive integer n (1 ≤ n ≤ 105) — the number of the available sticks.

The second line of the input contains n positive integers li (2 ≤ li ≤ 106) — the lengths of the sticks.

Output

The first line of the output must contain a single non-negative integer — the maximum total area of the rectangles that Ilya can make from the available sticks.

Examples

Input

4
2 4 4 2


Output

8


Input

4
2 2 3 5


Output

0


Input

4
100003 100004 100005 100006


Output

10000800015
/*
 * Author- Priyam Vora
 * BTech 2nd Year DAIICT
 */

        import java.io.*;
     
        import java.math.BigInteger;
        import java.util.*;
import java.util.Map.Entry;

import javax.print.attribute.SetOfIntegerSyntax;
     
        public class Graph1 {
        	
    	    private static InputStream stream;
        	private static byte[] buf=new byte[1024];
        	private static int curChar;
        	private static int numChars;
        	private static SpaceCharFilter filter;
        	private static PrintWriter pw;
        	private static long count=0;
            public static void main(String args[] ) throws Exception 
            {
            	InputReader(System.in);
        		pw=new PrintWriter(System.out);
        		//ans();
        		soln();
        		pw.close();
            }
     
            public static long gcd(long x,long y)
            {
            	if(x%y==0)
            		return y;
            	else
            		return gcd(y,x%y);
            }
            public static int gcd(int x,int y)
            {
            	if(x%y==0)
            		return y;
            	else 
            		return gcd(y,x%y);
            }
            


public static long pow(long n,long p,long m)
{
	 long  result = 1;
	  if(p==0)
	    return 1;
	if (p==1)
	    return n;
	while(p!=0)
	{
	    if(p%2==1)
	        result *= n;
	    if(result>=m)
	    result%=m;
	    p >>=1;
	    n*=n;
	    if(n>=m)
	    n%=m;
	}
	return result;
}
public static long pow(long n,long p)
{
	long  result = 1;
	  if(p==0)
	    return 1;
	if (p==1)
	    return n;
	while(p!=0)
	{
	    if(p%2==1)
	        result *= n;	    
	    p >>=1;
	    n*=n;	    
	}
	return result;

}
public static boolean printSubsets(int set[],int pow)
	{
		int n = set.length;

		// Run a loop for printing all 2^n
		// subsets one by obe
		for (int i = 0; i < (1<<n); i++)
		{
			int a[]=new int[n];
			
			int count=0;

			// Print current subset
			for (int j = 0; j < n; j++)

				// (1<<j) is a number with jth bit 1
				// so when we 'and' them with the
				// subset number we get which numbers
				// are present in the subset and which
				// are not
				if ((i & (1 << j)) > 0)
					{
					
					a[count]=set[j];
					count++;
					//System.out.print(set[j] + " ");
					}
int sum=0;
		for(int t=0;t<count;t++){
		sum+=a[t];	
			//pw.print(a[t]+" ");
		}
		if(sum==pow){
		return true;
		}
		}
		return false;
		//System.out.println(sum+"-sum "+l+" -l");
		}

	 
	// remove N elements in equal steps starting at specific point
	static List<Integer> josephus(int N, int step, int start)
	{
	    if (N < 1 || step < 1 || start < 1) return null;

	    List<Integer> p = new LinkedList<Integer>();
	    for (int i = 0; i < N; i++)
	        p.add(i+1);

	    List<Integer> r = new LinkedList<Integer>();
	    int i = (start - 2) % N;
	    for (int j = N; j > 0; j--) {
	        i = (i + step) % N--;
	        r.add(p.remove(i--));
	    }

	    return r;
	}

	 
	 
	 public static long fact(long n){
		 if(n==0)
			 return 1;
		 else
			 return (long)n*(long)fact(n-1);
		 
	 }


public static int[] radixSort(int[] f)
{
	int[] to = new int[f.length];
	{
		int[] b = new int[65537];
		for(int i = 0;i < f.length;i++)b[1+(f[i]&0xffff)]++;
		for(int i = 1;i <= 65536;i++)b[i]+=b[i-1];
		for(int i = 0;i < f.length;i++)to[b[f[i]&0xffff]++] = f[i];
		int[] d = f; f = to;to = d;
	}
	{
		int[] b = new int[65537];
		for(int i = 0;i < f.length;i++)b[1+(f[i]>>>16)]++;
		for(int i = 1;i <= 65536;i++)b[i]+=b[i-1];
		for(int i = 0;i < f.length;i++)to[b[f[i]>>>16]++] = f[i];
		int[] d = f; f = to;to = d;
	}
	return f;
} 

public static int nextPowerOf2(final int a)
{
    int b = 1;
    while (b < a)
    {
        b = b << 1;
    }
    return b;
}
     
        
    public static boolean PointInTriangle(int p1, int p2, int p3, int p4, int p5, int p6, int p7, int p8)
    {
    int s = p2 * p5 - p1 * p6 + (p6 - p2) * p7 + (p1 - p5) * p8;
    int t = p1 * p4 - p2 * p3 + (p2 - p4) * p7 + (p3 - p1) * p8;
     
    if ((s < 0) != (t < 0))
    return false;
     
    int A = -p4 * p5 + p2 * (p5 - p3) + p1 * (p4 - p6) + p3 * p6;
    if (A < 0.0)
    {
    s = -s;
    t = -t;
    A = -A;
    }
    return s > 0 && t > 0 && (s + t) <= A;
    }
     
      public static float area(int x1, int y1, int x2, int y2, int x3, int y3){
    	  return (float)Math.abs((x1*(y2-y3) + x2*(y3-y1)+ x3*(y1-y2))/2.0);
      }
      public static boolean isPrime(int n)
      {
          // Corner cases
          if (n <= 1)  return false;
          if (n <= 3)  return true;
       
          // This is checked so that we can skip 
          // middle five numbers in below loop
          if (n%2 == 0 || n%3 == 0) return false;
       
          for (int i=5; i*i<=n; i=i+6)
              if (n%i == 0 || n%(i+2) == 0)
                 return false;
       
          return true;
      }
     
     
    //merge Sort
            
            public static void Merge_sort(int a[]){
            	int len=a.length;
            	if(len <2)
            		return ;
            	int mid=len/2;
            	int l[]=new int[mid];
            	int r[] =new int[len-mid];
            	for(int i=0;i<mid;i++)
            		l[i]=a[i];
            	for(int i=mid;i<len;i++)
            		r[i-mid]=a[i];
            	
            	Merge_sort(l);
            	Merge_sort(r);
            	Merge(l,r,a);
            }
            	
            public static void Merge(int []l,int[]r,int a[]){
            	int nl=l.length;
            	int nr=r.length;
            	int i=0,j=0,k=0;
            	
            	while(i <nl && j<nr){
            		if(l[i] > r[j]){
            			a[k]=l[i];
            			k++;
            			i++;
            		}
            		else{
            			a[k]=r[j];
            			k++;
            			j++;
            		}
            		
            		while(i<nl){
            			a[k]=l[i];
            			k++;
            			i++;
            		}
            		while(j<nr){
            			a[k]=r[j];
            			k++;
            			j++;
            		}
            	}
            }
      
        	
        public static boolean isSubSequence(String large,String small,int largeLen,int smallLen){
        //base cases
        	if(largeLen==0)
        		return false;
        	if(smallLen==0)
        		return true;
        	  // If last characters of two strings are matching
        	if(large.charAt(largeLen-1)==small.charAt(smallLen-1))
        		isSubSequence(large, small, largeLen-1, smallLen-1);
        	// If last characters are not matching
        	return isSubSequence(large, small, largeLen-1, smallLen);
        }
     
        // To Get Input
         	// Some Buffer Methods
         
         	public static void InputReader(InputStream stream1) {
         		stream = stream1;
         	}
         
         	private static boolean isWhitespace(int c) {
         		return c == ' ' || c == '\n' || c == '\r' || c == '\t' || c == -1;
         	}
         
         	private static boolean isEndOfLine(int c) {
         		return c == '\n' || c == '\r' || c == -1;
         	}
         
         	private static int read() {
         		if (numChars == -1)
         			throw new InputMismatchException();
         		if (curChar >= numChars) {
         			curChar = 0;
         			try {
         				numChars = stream.read(buf);
         			} catch (IOException e) {
         				throw new InputMismatchException();
         			}
         			if (numChars <= 0)
         				return -1;
         		}
         		return buf[curChar++];
         	}
         
         	private static int nextInt() {
         		int c = read();
         		while (isSpaceChar(c))
         			c = read();
         		int sgn = 1;
         		if (c == '-') {
         			sgn = -1;
         			c = read();
         		}
         		int res = 0;
         		do {
         			if (c < '0' || c > '9')
         				throw new InputMismatchException();
         			res *= 10;
         			res += c - '0';
         			c = read();
         		} while (!isSpaceChar(c));
         		return res * sgn;
         	}
          
         	private static long nextLong() {
         		int c = read();
         		while (isSpaceChar(c))
         			c = read();
         		int sgn = 1;
         		if (c == '-') {
         			sgn = -1;
         			c = read();
         		}
         		long res = 0;
         		do {
         			if (c < '0' || c > '9')
         				throw new InputMismatchException();
         			res *= 10;
         			res += c - '0';
         			c = read();
         		} while (!isSpaceChar(c));
         		return res * sgn;
         	}
          
         	private static String nextToken() {
         		int c = read();
         		while (isSpaceChar(c))
         			c = read();
         		StringBuilder res = new StringBuilder();
         		do {
         			res.appendCodePoint(c);
         			c = read();
         		} while (!isSpaceChar(c));
         		return res.toString();
         	}
          
         	private static String nextLine() {
         		int c = read();
         		while (isSpaceChar(c))
         			c = read();
         		StringBuilder res = new StringBuilder();
         		do {
         			res.appendCodePoint(c);
         			c = read();
         		} while (!isEndOfLine(c));
         		return res.toString();
         	}
         
         	private static int[] nextIntArray(int n) {
         		int[] arr = new int[n];
         		for (int i = 0; i < n; i++) {
         			arr[i] = nextInt();
         		}
         		return arr;
         	}
         	  
         	private static long[] nextLongArray(int n) {
         		long[] arr = new long[n];
         		for (int i = 0; i < n; i++) {
         			arr[i] = nextLong();
         		}
         		return arr;
         	}
         
         	private static void pArray(int[] arr){
         		for (int i=0; i<arr.length; i++) {
         			System.out.print(arr[i] + " ");
         		}
         		System.out.println();
         		return;
         	}
         
         	private static void pArray(long[] arr){
         		for (int i=0; i<arr.length; i++) {
         			System.out.print(arr[i] + " ");
         		}
         		System.out.println();
         		return;		
         	}
         	
         	private static void pArray(boolean[] arr){
         		for (int i=0; i<arr.length; i++) {
         			System.out.print(arr[i] + " ");
         		}
         		System.out.println();
         		return;
         	}
     
         
         	private static boolean isSpaceChar(int c) {
         		if (filter != null)
         			return filter.isSpaceChar(c);
         		return isWhitespace(c);
         	}
          
         	private interface SpaceCharFilter {
         		public boolean isSpaceChar(int ch);
         	}
         	private static int GetRightPosition(int A[], int l, int r, int key)
         	{
         	    int m;
         	 
         	    while( r - l > 1 )
         	    {
         	        m = l + (r - l)/2;
         	 
         	        if( A[m] <= key )
         	            l = m;
         	        else
         	            r = m;
         	    }
         	 
         	    return l;
         	}
         	 
         	private static int GetLeftPosition(int A[], int l, int r, int key)
         	{
         	    int m;
         	 
         	    while( r - l > 1 )
         	    {
         	        m = l + (r - l)/2;
         	 
         	        if( A[m] >= key )
         	            r = m;
         	        else
         	            l = m;
         	    }
         	 
         	    return r;
         	}
         	 
         	private static int CountOccurances(int A[], int size, int key)
         	{
         	    // Observe boundary conditions
         	    int left = GetLeftPosition(A, -1, size-1, key);
         	    int right = GetRightPosition(A, 0, size, key);
         	 
         	    // What if the element doesn't exists in the array?
         	    // The checks helps to trace that element exists
         	    return (A[left] == key && key == A[right])?
         	           (right - left + 1) : 0;
         	}	private static int Floor(int a[],int low,int high,int target,int ans){
         	
         		if(a[high]<target){
         			return a[high];
         		}
         		if(a[low]>target){
         			return -1;
         		}
         		
         		while(high-low>1){
         		int mid=low+(high-low)/2;
         		if(a[mid]==target)
         			return a[mid];
         		if(a[mid]>=target){
         			
         			high=mid;
         		}
         		else{
         			if(ans<a[mid])
         				ans=a[mid];
         			low=mid;
         			
         		}
         		}
         		return ans;
         		}
         	private static int Ceil(int arr[], int low, int high, int x)
         	{
         	int mid; 

         	
         	/* If x is smaller than or equal to the first element,
         		then return the first element */
         	if(x <= arr[low])
         		return low; 

         	/* If x is greater than the last element, then return -1 */
         	if(x > arr[high])
         		return -1; 

         	/* get the index of middle element of arr[low..high]*/
         	mid =  low + (high - low)/2;
         	System.out.println(mid+")))");
         	/* If x is same as middle element, then return mid */
         	if(arr[mid] == x)
         		return mid;
         		
         	/* If x is greater than arr[mid], then either arr[mid + 1]
         		is ceiling of x or ceiling lies in arr[mid+1...high] */
         	else if(arr[mid] < x)
         	{
         		if(mid + 1 <= high && x <= arr[mid+1])
         		return mid + 1;
         		else
         		return Ceil(arr, mid+1, high, x);
         	}

         	/* If x is smaller than arr[mid], then either arr[mid] 
         		is ceiling of x or ceiling lies in arr[mid-1...high] */
         	else
         	{
         		if(mid - 1 >= low && x > arr[mid-1])
         		return mid;
         		else	
         		return Ceil(arr, low, mid - 1, x);
         	}
         	}
         	private static int BinarySearch(int a[],int low,int high,int target){
         		if(low>high)
         			{return -1;} 
         		
         		int mid=low+(high-low)/2;
         		if(target==a[mid])
         			{
         			while(mid<a.length){
         				if(a[mid]!=target)
         				{
         					break;
         				}
         				mid++;
         			}
         			mid--;
         			return mid;
         			}
         		if(target > a[mid]){
         			low=mid+1;
         		}
         		if(target < a[mid]){
         			high=mid-1;
         		}
         		return BinarySearch(a, low, high, target);
         	}
         //	-----------------------My Code-----------------------------------------
         	 private static void soln() {
 
         		 int n=nextInt();
         		 int a[]=nextIntArray(n);
         		 Arrays.sort(a);
         		 long f1=0,f2=0,c1=0,c2=0,ans=0;
         		 for(int i=(n-1);i>=1;i--){
         			 int diff1=Math.abs(a[i]-a[i-1]);
         			//int diff2=Math.abs(a[i-2]-a[i-3]);
        			  
         			 if(diff1<=1){

         				 if(diff1==0){
         					 if(c1==0){

             					 f1=a[i];
             					 c1=1; 
         					 }
         					 else{
         						 f2=a[i];
         						 c2=1;
         					 }
         				 }else{
         					 if(c1==0){
         						 f1=a[i]-1;
                 				 c1=1;		 
         					 }else{
         						 f2=a[i]-1;
         						 c2=1;
         					 }
         				}
         				 if(c1==1 && c2==1){
         					 ans+=(f1*f2);
         					// System.out.println(f1+" "+f2);
         					 //System.out.println(f1*f2+"ind");
         					 c1=0;
         					 c2=0;
         					 //System.exit(0);
         				 }
         			 i--;
         			 }
         		 }
         		 System.out.println(ans);
         		 
       
         	 
         		 	  
          	 }
         	 
         	// ------------------------------THE END-----------------------------------
         	
         	        }
        
        class MyComp implements Comparator<Integer>{

			@Override
			public int compare(Integer arg0, Integer arg1) {
			return arg1.compareTo(arg0);
				// TODO Auto-generated method stub
					}
        	
        }
        class Graph{
        	private long conse=0,co=0,mac_cons_cat=0;
        	private int V,flag=1, d[], road_cond[][];
        	private Stack <Integer>st=new Stack();
        	private LinkedList<Integer > adj[];
        //	boolean Visited[];
        	Graph(int V){
        		V++;
        
        		
        		//this.mac_cons_cat=max_cat;
        		this.V=(V);
        		adj=new LinkedList[V];
        		//for(int i=0;i<V;i++)
        			//adj[i]=new LinkedList();
        		
        			
        		//Visited=new boolean[V];
        	 
        	}
        	void addEdge(int v,int w){
        		if(adj[v]==null){
        			adj[v]=new LinkedList();
        		}
        		adj[v].add(w);
        	
        	}
        	public long  bfs(int s)
            {
        		co=0;
                // Mark all the vertices as not visited(By default
                // set as false)
                boolean visited[] = new boolean[V];
         
                // Create a queue for BFS
                LinkedList<Integer> queue = new LinkedList<Integer>();
         
                // Mark the current node as visited and enqueue it
                visited[s]=true;
                queue.add(s);
         
                while (queue.size() != 0)
                {
                    // Dequeue a vertex from queue and print it
                    s = queue.poll();
                   // System.out.print(s+" ");
         
                    // Get all adjacent vertices of the dequeued vertex s
                    // If a adjacent has not been visited, then mark it
                    // visited and enqueue it
                    Iterator<Integer> i = adj[s].listIterator();
                    while (i.hasNext())
                    {
                        int n = i.next();
                        if (!visited[n])
                        {
                            visited[n] = true;
                            queue.add(n);
                        co++;
                        }
                    }
                    return co;
                }
                return 0;
            }
        	 public long  dfs(int startVertex){
        		
        		boolean Visited[]=new boolean[V];
        		
        		//flag=1;
        		
        		 if(!Visited[startVertex])  {
        			
        			 co=0; 
        			 dfsUtil(startVertex,Visited);
           		 
        		 }
        		 
        		 return co;
        	 }
        	 public void Connected(int v){
        		 Iterator<Integer> i = adj[v].listIterator();
        		 while(i.hasNext()){
        			 int n=i.next();
        			 long data=(long)d[n]+(long)d[v];
        			 data=data%1000000007;
        			 d[n]=(int)data;
        		 }
        	 }
        	 public int getByte(int v){
        		 return d[v];
        	 }
        	private void dfsUtil(int startVertex, boolean[] Visited) {
        		//System.out.println(pre+" "+startVertex);
        		
        		Visited[startVertex]=true;
        		
        		
        		st.push(startVertex);
        		while(!st.isEmpty()){
        			int top=st.pop();
        			System.out.print(top+" ");
        			
        			//System.out.println(top);
        		Iterator<Integer> i=adj[top].listIterator();
        	
        		while(i.hasNext()){
        			int n=i.next();
        		//	System.out.println(n+"---");
        			 if( !Visited[n]){
        				Visited[n]=true;
        					st.push(n);
        					co++;
        					}
        			 }
        		
        	}
        		}
        }

        class Dsu{
        	private int rank[], parent[] ,n;
        	
        	Dsu(int size){
        		this.n=size+1;
        		rank=new int[n];
        		parent=new int[n];
        	makeSet();
        	}
        	
        	void makeSet(){
        		for(int i=0;i<n;i++){
        			parent[i]=i;
        		}
        	}
        	
        	int find(int x){
        		if(parent[x]!=x){
        			
        			parent[x]=find(parent[x]);
        		}
        		return parent[x];
        	}	
        	
        	void union(int x,int y){
        		int xRoot=find(x);
        		int yRoot=find(y);
        		
        		if(xRoot==yRoot)
        			return;
        		if(rank[xRoot]<rank[yRoot]){
        		parent[xRoot]=yRoot;	
        		}else if(rank[yRoot]<rank[xRoot]){
        			parent[yRoot]=xRoot;
        		}else{
        			parent[yRoot]=xRoot;
        			rank[xRoot]++;
        		}
        		
        	}
        }


