// Source: https://usaco.guide/general/io

#include <bits/stdc++.h>
using namespace std;
#define int long long

signed main() {
	int n,x;cin>>n>>x;
	int s3=0,sk=0;
	while(n--){
		int a;cin>>a;
		sk+=a%x;
		a-=a%x;
		s3+=a/x;
	}
	if(s3>=sk){
		int ss=sk;
		s3-=sk;
		ss+=s3/(x+1);
		cout<<ss/2<<endl;
	}
	else{
		cout<<s3<<endl;
	}
}