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


int main() {
    /* Enter your code here. Read input from STDIN. Print output to STDOUT */
    int n,k;
    cin>>n>>k;
    long a[n],dp[n],i;
    for(i=0;i<n;i++)
        cin>>a[i];
    for(i=0;i<=k && i<n;i++)
    dp[i]=a[i];
    for(;i<n;i++)
        {
        dp[i]=a[i]+a[i-k-1];
    }
    cout<<dp[n-1];
    return 0;
}