#include <iostream>
using namespace std;

int main()
{
    int n,m;
    cin >> n >> m;
    int sum=0,minn = 1e9,cnt=0;
    for(int i = 1;i <= n;i++)
    {
        int a;
        cnt++;
        cin >> a;
        sum += a;
        if(cnt == m)
        {
            cnt = 0;
            minn = min(sum,minn);
            sum = 0;
        }
        
    }
    if(minn != 1e9)
    cout << minn << endl;
    else
    cout << 0 << endl;
    
    return 0;
}