789A - Anastasia and pebbles - CodeForces Solution

#include <bits/stdc++.h>
#define ll long long
#define ld long double
#define fast ios_base::sync_with_stdio(false);cin.tie(nullptr);cout.tie(nullptr);
#define all(x) x.begin(),x.end()
#define yes cout << "YES\n" ;
#define no cout << "NO\n" ;
using namespace std ;
const ll mod = 1e9+7 ; const int oo = 0x3f3f3f3f;
int dy[] = {+0, +0, -1, 1};
int dx[] = {-1, 1, +0, +0};
const int N=2e5+10;

int main() {
    // freopen("input.txt","r",stdin);
    // freopen("output.txt","w",stdout);
    fast
    int tt = 1;
    //cin >> tt;
    while (tt--) {
        ll n,k;
        cin >> n >> k ;
        vector<ll>v(n);
        for ( int i=0; i<n; i++ ) {
            cin >> v[i] ;
        }
        sort(v.begin(),v.end());
        ll ans=0,sum=0;
        for ( int i=0; i<n; i++ ) {
            sum+= ceil((double )v[i]/k);
        }
        ans = ceil((double)sum/2);
        cout << ans ;

    }
}