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


int main() {
    long long int i,j,k=0,l=0,m,n,o,p=100000000000;
    cin>>n>>k;long long int a[n];
    for(i=0;i<n;++i)
    {cin>>a[i];if(p>a[i])p=a[i];}
    if((2*k+1)>=n){cout<<p;return 0;}
    for(i=k;i<n;){l+=a[i];i+=k;}cout<<l;
    /* Enter your code here. Read input from STDIN. Print output to STDOUT */   
    return 0;
}