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
//package code;
import java.io.*;
import java.util.*;
import java.util.Map.Entry;
import java.text.*;
import java.math.*;
import java.util.regex.*;
import java.awt.Point;
/**
 *
 * @author prabhat // use stringbuilder,TreeSet, priorityQueue, x+y=(x&y + x|y);
 */
   public class  a
   {
   public static int n,max1=100005,k,m,q,set[];
   public static Point[] p1,p2;
   public static long mod=(long)1e9+7,nCr[][],dp[][][],pre[][],suf[][],a[];
   public static boolean[] isPrime;
   public static  ArrayList<Integer> divisor[],prime,adj[];
   public  static BufferedReader br=new BufferedReader(new InputStreamReader(System.in));
   static PrintWriter pw;
   public  static void main(String[] args) throws Exception
   {
   	     InputReader in = new InputReader(System.in);
		 pw=new PrintWriter(System.out);
		 n=in.ii();
		 int[]a=in.iia(n);
		 Arrays.sort(a);
		 long ans=0;
		
		for(int i=n-1;i>2;i-=2)
		 {
			 long x=0;
			 long y=0;
			while(i>0&&a[i]-a[i-1]>1)i--;
			if(i>0)
			{
				x=Math.min(a[i],a[i-1]);
			}
			i-=2;
			while(i>0&&a[i]-a[i-1]>1)i--;
			if(i>0)
			{
				y=Math.min(a[i],a[i-1]);
			}
            ans+=x*y*1l;
		 }
		 pw.println(ans);
		 pw.close();
   }
  
   static class Pair{
	   int x;int y;
	   Pair(int a,int b)
	   {
		   x=a;
		   y=b;
	   }
   }
  
static long ncr(int i,int  j)
{
 if(j==0||i==j)return 1;
 if(nCr[i][j]!=-1)return nCr[i][j];
 long res=ncr(i-1,j-1)+ncr(i-1,j);
 return nCr[i][j]=res;
}
public  static class DSU
{
	int[] parent;
	int[] rank;
	int cnt;
	public DSU(int n){
		parent=new int[n];
		rank=new int[n];
		for(int i=0;i<n;i++){
			parent[i]=i;
			rank[i]=1;
		}
		cnt=n;
	}
	int find(int i){
		while(parent[i] !=i){
			parent[i]=parent[parent[i]];
			i=parent[i];
		}
		return i;
	}
	int Union(int x, int y){
		int xset = find(x);
		int yset = find(y);
		if(xset!=yset)
			cnt--;
		if(rank[xset]<rank[yset]){
			parent[xset] = yset;
			rank[yset]+=rank[xset];
			rank[xset]=0;
			return yset;
		}else{
			parent[yset]=xset;
			rank[xset]+=rank[yset];
			rank[yset]=0;
			return xset;
		}
	}
}

static int gcd(int a,int b)
{
	while(a!=0)
	{
		int temp=a;
		a=b%a;
		b=temp;
	}
	return b;
}
static void Seive()
{
	isPrime=new boolean[max1];
	Arrays.fill(isPrime,true);
	prime=new ArrayList<>();
	divisor=new ArrayList[max1];
	for(int i=1;i<max1;i++)divisor[i]=new ArrayList<Integer>();
    isPrime[0]=isPrime[1]=false;
	for(int i=2;i<(max1);i++)
	{
         if(isPrime[i]){
			 divisor[i].add(i);
			 prime.add(i);
			for(int j=2*i;j<max1;j+=i)
			{
				isPrime[j]=false;
				divisor[j].add(i);
			}
		}
	}
}
public static long pow(long n,long p)
{
	 long  result = 1;
	  if(p==0)
	    return 1;

	while(p!=0)
	{
	    if(p%2==1)
	        result *= n;
	    
	    p >>=1;
	    n*=n;
	}
	return result;
}


static  class InputReader
{
   private InputStream stream;
   private byte[] buf = new byte[1024];

   private SpaceCharFilter filter;
    byte inbuffer[] = new byte[1024];
   int lenbuffer = 0, ptrbuffer = 0;
    final int M = (int) 1e9 + 7;
   int md=(int)(1e7+1);
    int[] SMP=new int[md];
   final double eps = 1e-6;
   final double pi = Math.PI;

	PrintWriter out;
   String check = "";
 InputStream   obj = check.isEmpty() ? System.in : new ByteArrayInputStream(check.getBytes());
   public InputReader(InputStream stream)
   {
       this.stream = stream;
   }

    int readByte() {
	        if (lenbuffer == -1) throw new InputMismatchException();
	        if (ptrbuffer >= lenbuffer) {
	            ptrbuffer = 0;
	            try {
	                lenbuffer = obj.read(inbuffer);
	            } catch (IOException e) {
	                throw new InputMismatchException();
	            }
	        }
	        if (lenbuffer <= 0) return -1;
	        return inbuffer[ptrbuffer++];
   }

   public  int read()
   {
       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;
   }

   String is() {
	        int b = skip();
	        StringBuilder sb = new StringBuilder();
	        while (!(isSpaceChar(b))) // when nextLine, (isSpaceChar(b) && b!=' ')
	        {
	            sb.appendCodePoint(b);
	            b = readByte();
	        }
	        return sb.toString();
   }
   public   int ii() {
	        int num = 0, b;
	        boolean minus = false;
	        while ((b = readByte()) != -1 && !((b >= '0' && b <= '9') || b == '-')) ;
	        if (b == '-') {
	            minus = true;
	            b = readByte();
	        }
	        while (true) {
	            if (b >= '0' && b <= '9') {
	                num = num * 10 + (b - '0');
	            } else {
	                return minus ? -num : num;
	            }
	            b = readByte();
	        }
   }
 public   long il() {
	        long num = 0;
	        int b;
	        boolean minus = false;
	        while ((b = readByte()) != -1 && !((b >= '0' && b <= '9') || b == '-')) ;
	        if (b == '-') {
	            minus = true;
	            b = readByte();
	        }
	        while (true) {
	            if (b >= '0' && b <= '9') {
	                num = num * 10 + (b - '0');
	            } else {
	                return minus ? -num : num;
	            }
	            b = readByte();
	        }
   }

	    boolean isSpaceChar(int c) {
	        return (!(c >= 33 && c <= 126));
	       }

	      int skip()
	        {
	        int b;
	        while ((b = readByte()) != -1 && isSpaceChar(b)) ;
	        return b;
	        }

	    float nf() {
	        return Float.parseFloat(is());
	    }

	    double id() {
	        return Double.parseDouble(is());
	    }

	    char ic() {
	        return (char) skip();
	    }

	    int[] iia(int n) {
	        int a[] = new int[n];
	        for (int i = 0; i<n; i++) a[i] = ii();
	        return a;
	    }

	    long[] ila(int n) {
	        long a[] = new long[n];
	        for (int i = 0; i <n; i++) a[i] = il();
	        return a;
	    }

	    String[] isa(int n) {
	        String a[] = new String[n];
	        for (int i = 0; i < n; i++) a[i] = is();
	        return a;
	    }


		 long mul(long a, long b) { return a * b % M; }

		/*	long div(long a, long b)
				 {
					return mul(a, pow(b, M - 2,M));

		           }
*/


	    double[][] idm(int n, int m) {
	        double a[][] = new double[n][m];
	        for (int i = 0; i < n; i++) for (int j = 0; j < m; j++) a[i][j] = id();
	        return a;
	        }

	    int[][] iim(int n, int m) {
	        int a[][] = new int[n][m];
	        for (int i = 0; i < n; i++) for (int j = 0; j <m; j++) a[i][j] = ii();
	        return a;
          }


   public String readLine() {
       int c = read();
       while (isSpaceChar(c))
           c = read();
       StringBuilder res = new StringBuilder();
       do {
           res.appendCodePoint(c);
           c = read();
       } while (!isEndOfLine(c));
       return res.toString();
   }

   public interface SpaceCharFilter
   {
       public boolean isSpaceChar(int ch);
   }
   public boolean isEndOfLine(int c) {
       return c == '\n' || c == '\r' || c == -1;
   }
}

}
