#include <cmath>
#include <cstdio>
#include <vector>
#include <iostream>
#include <algorithm>
using namespace std;
#define ll long long

int main() {
    /* Enter your code here. Read input from STDIN. Print output to STDOUT */  
    ll n,k,i,j,m;
    cin>>n>>k;
    ll a[n];
    ll s=0;
    for(i=0;i<n;i++)
        {
        cin>>a[i];
        s+=a[i];
    }
    if(k==0)
        {
        cout<<s;
    }
    else 
        {
       ll q=0;
        for(i=k;i<n;i+=k+1)
            {
            q+=a[i];
        }
        cout<<q;
    }
    return 0;
}