Anastasia loves going for a walk in Central Uzhlyandian Park. But she became uninterested in simple walking, so she began to collect Uzhlyandian pebbles. At first, she decided to collect all the pebbles she could find in the park.

She has only two pockets. She can put at most k pebbles in each pocket at the same time. There are n different pebble types in the park, and there are wi pebbles of the i-th type. Anastasia is very responsible, so she never mixes pebbles of different types in same pocket. However, she can put different kinds of pebbles in different pockets at the same time. Unfortunately, she can't spend all her time collecting pebbles, so she can collect pebbles from the park only once a day.

Help her to find the minimum number of days needed to collect all the pebbles of Uzhlyandian Central Park, taking into consideration that Anastasia can't place pebbles of different types in same pocket.

Input

The first line contains two integers n and k (1 ≤ n ≤ 105, 1 ≤ k ≤ 109) — the number of different pebble types and number of pebbles Anastasia can place in one pocket.

The second line contains n integers w1, w2, ..., wn (1 ≤ wi ≤ 104) — number of pebbles of each type. 

Output

The only line of output contains one integer — the minimum number of days Anastasia needs to collect all the pebbles.

Examples

Input

3 2
2 3 4


Output

3


Input

5 4
3 1 8 9 7


Output

5

Note

In the first sample case, Anastasia can collect all pebbles of the first type on the first day, of second type — on the second day, and of third type — on the third day.

Optimal sequence of actions in the second sample case: 

  * In the first day Anastasia collects 8 pebbles of the third type. 
  * In the second day she collects 8 pebbles of the fourth type. 
  * In the third day she collects 3 pebbles of the first type and 1 pebble of the fourth type. 
  * In the fourth day she collects 7 pebbles of the fifth type. 
  * In the fifth day she collects 1 pebble of the second type. 
import java.util.*;
import java.io.*;
import java.math.*;
public class Fuck{
	static long MOD=(long)Math.pow(10,9)+7;
	static final int lint=Integer.MAX_VALUE;
	static final double ldouble=Double.MAX_VALUE;
	public static void main(String args[]) {
        new Thread(null, new Runnable() {
            public void run() {
                try{
                    solve();
                }
                catch(Exception e){
                    e.printStackTrace();
                }
            }
        }, "1", 1 << 26).start();
	}
    static InputReader in;
    static PrintWriter w;
    static void solve(){
        in = new InputReader(System.in);
        w = new PrintWriter(System.out);
        int n=in.nextInt();
        int k=in.nextInt();
        int arr[]=new int[n];
        int lt=0;
        for(int i=0;i<n;i++){
        	arr[i]=in.nextInt();
        	if(arr[i]<=k){
        		lt++;
        	}
        	else if(arr[i]>k&&arr[i]<=2*k){
        		lt+=2;
        	}
        	else{
        		lt+=(arr[i]/(k));
        		if(arr[i]%k>0){
        			lt++;
        		}
        	}
        }
        w.println((lt/2)+(lt%2));
        w.close();
    }
    
//  //if  str2 (pattern) is subsequence of str1 (Text) or not
//	static boolean function(String str1,String str2){
//	     str2 = str2.replace("", ".*");  //returns .*a.*n.*n.*a.
//	     return (str1.matches(str2));  // returns true
//	}
    static double convert(double a){
    	return Math.round(a * 100.0) / 100.0;
    }
    static boolean flag=false;
    static HashSet<Integer> ans;
    static int Arr[];
    static long size[];
  //modified initialize function:
    static void initialize(int N){
    	Arr=new int[N];
    	size=new long[N];
        for(int i = 0;i<N;i++){
        	Arr[ i ] = i ;
        	size[ i ] = 1;
        }
    }
    static boolean find(int A,int B){
        if( root(A)==root(B) )       //if A and B have same root,means they are connected.
        return true;
        else
        return false;
    }
 // modified root function.
    static void weighted_union(int A,int B,int n){
        int root_A = root(A);
        int root_B = root(B);
        if(size[root_A] < size[root_B ]){
        	Arr[ root_A ] = Arr[root_B];
        	size[root_B] += size[root_A];
        }
        else{
        	Arr[ root_B ] = Arr[root_A];
        	size[root_A] += size[root_B];
        }
    }
    static int root (int i){
        while(Arr[ i ] != i){
            Arr[ i ] = Arr[ Arr[ i ] ] ; 
            i = Arr[ i ]; 
        }
        return i;
    }
    
//	static long gcd(long a,long b){
//		if(a==0){
//			return b;
//		}
//		return gcd(b%a,a);
//	}
//	static boolean isPrime[];
////	 //for marking all prime numbers greater than 1 and less than equal to N
//	static void sieve(int N) {
//      isPrime=new boolean[N+1];
//      isPrime[0] = true;
//      isPrime[1] = true;
//      for(int i = 2; i * i <= N; ++i) {
//           if(isPrime[i] == false) {//Mark all the multiples of i as composite numbers
//               for(int j = i * i; j <= N ;j += i)
//                   isPrime[j] = true;
//          }
//      }
//	}
//	static boolean isPrime(long n) {
//		if(n < 2L) return false;
//		if(n == 2L || n == 3L) return true;
//		if(n%2L == 0 || n%3L == 0) return false;	
//		long sqrtN = (long)Math.sqrt(n)+1L;
//		for(long i = 6L; i <= sqrtN; i += 6L) {
//			if(n%(i-1) == 0 || n%(i+1) == 0) return false;
//		}
//		return true;
//	}
//	static HashMap<Integer,Integer> level;;
//	static HashMap<Integer,Integer> parent;
	static int maxlevel=0;
	static ArrayList<Integer> adj[]; //Adjacency Lists
    static int V;   // No. of vertices
    // Constructor
    static void Graph(int v){
        V = v;
        adj = new ArrayList[v];
        for (int i=0; i<v; ++i){
        	adj[i] = new ArrayList();
        }
    }
    // Function to add an edge into the graph
    static void addEdge(int v,int w){
		adj[v].add(w);
//		adj[w].add(v);
    }
    static void bfs(int s,int n){
    	boolean visited[]=new boolean[n];
    	LinkedList<Integer> queue=new LinkedList<Integer>();
    	queue.add(s);
    	visited[s]=true;
    	ans.add(s);
    	while(!queue.isEmpty()){
    		int num=queue.pop();
//    		System.out.println(ans.toString());
    		if(flag){
    			break;
    		}
    		for(int i=0;i<adj[num].size();i++){
    			if(!visited[adj[num].get(i)]){
    				visited[adj[num].get(i)]=true;
    				queue.add(adj[num].get(i));
    				ans.add(adj[num].get(i));
    				if(ans.size()==n){
    					flag=true;
    					break;
    				}
    			}
    		}
    	}
    }
//	static boolean T[][][];
//	static void subsetSum(int input[], int total, int count) {
//        T = new boolean[input.length + 1][total + 1][count+1];
//        for (int i = 0; i <= input.length; i++) {
//        	T[i][0][0] = true;
//        	for(int j = 1; j<=count; j++){
//        		T[i][0][j] = false;
//        	}
//        }
//        int sum[]=new int[input.length+1];
//        for(int i=1;i<=input.length;i++){
//            sum[i]=sum[i-1]+input[i-1];
//        }
//        for (int i = 1; i <= input.length; i++) {
//            for (int j = 1; j <= (int)Math.min(total,sum[i]); j++) {
//            	for (int k = 1; k <= (int)Math.min(i,count); k++){
//            		 if (j >= input[i - 1]) {//Exclude and Include
//                         T[i][j][k] = T[i - 1][j][k] || T[i - 1][j - input[i - 1]][k-1];
//                     } else {
//                         T[i][j][k] = T[i-1][j][k];
//                     }
//            	}
//            }
//        }
//    }
//	static <K,V extends Comparable<? super V>>
//	SortedSet<Map.Entry<K,V>> entriesSortedByValues(Map<K,V> map) {
//	    SortedSet<Map.Entry<K,V>> sortedEntries = new TreeSet<Map.Entry<K,V>>(
//	        new Comparator<Map.Entry<K,V>>() {
//	            @Override public int compare(Map.Entry<K,V> e1, Map.Entry<K,V> e2) {
//	                int res = e2.getValue().compareTo(e1.getValue());
//	                return res != 0 ? res : 1;
//	            }
//	        }
//	    );
//	    sortedEntries.addAll(map.entrySet());
//	    return sortedEntries;
//	}
	
 
	 
	//minimum prime factor of all the numbers less than n
    static int minPrime[];
	static void minimumPrime(int n){
		minPrime=new int[n+1];
		minPrime[1]=1;
        for (int i = 2; i * i <= n; ++i) {
            if (minPrime[i] == 0) {         //If i is prime
                for (int j = i * i; j <= n; j += i) {
                    if (minPrime[j] == 0) {
                        minPrime[j] = i;
                    }
                }
            }
        }
        for (int i = 2; i <= n; ++i) {
            if (minPrime[i] == 0) {
                minPrime[i] = i;
            }
        }
	}
	static long power(long base, long exponent, long modulus){
	    long result = 1;
	    while (exponent > 0) {
	        if (exponent % 2 == 1)
	            result = (result * base) % modulus;
	        exponent = exponent >> 1;
	        base = (base * base) % modulus;
	    }
	    return result;
	}
	static long modInverse(long A, long M)
	{
		long x=extendedEuclid(A,M)[0];
		return (x%M+M)%M;    //x may be negative
	}
	static long[] extendedEuclid(long A, long B) {
		if(B == 0) {
			long d = A;
			long x = 1;
			long y = 0;
			return new long[]{x,y,d};
		}
		else {
			long arr[]=extendedEuclid(B, A%B);
			long temp = arr[0];
			arr[0] = arr[1];
			arr[1] = temp - (A/B)*arr[1];
			return arr;
		}
	}
 
	static class InputReader {
        private final InputStream stream;
        private final byte[] buf = new byte[8192];
        private int curChar, numChars;
        private SpaceCharFilter filter;
 
        public InputReader(InputStream stream) {
            this.stream = stream;
        }
        
        public 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++];
        }
 
        public 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();
        }
 
        public String readString() {
            int c = read();
            while (isSpaceChar(c)) {
                c = read();
            }
            StringBuilder res = new StringBuilder();
            do {
                res.appendCodePoint(c);
                c = read();
            } while (!isSpaceChar(c));
            return res.toString();
        }
 
        public 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;
        }
 
        public 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;
        }
 
        public int[] nextIntArray(int n) {
            int[] arr = new int[n];
            for (int i = 0; i < n; i++) {
                arr[i] = nextInt();
            }
            return arr;
        }
 
        public long[] nextLongArray(int n) {
            long[] arr = new long[n];
            for (int i = 0; i < n; i++) {
                arr[i] = nextLong();
            }
            return arr;
        }
 
        public boolean isSpaceChar(int c) {
            if (filter != null)
                return filter.isSpaceChar(c);
            return c == ' ' || c == '\n' || c == '\r' || c == '\t' || c == -1;
        }
 
        private boolean isEndOfLine(int c) {
            return c == '\n' || c == '\r' || c == -1;
        }
        public interface SpaceCharFilter {
            public boolean isSpaceChar(int ch);
        }
	}
} 
class NodeS{
	char x;
	char y;
	public void setx(char x){
		this.x=x;
	}
	public void sety(char y){
		this.y=y;
	}
	public char getx(){
		return x;
	}
	public char gety(){
		return y;
	}
}