// https://www.luogu.com.cn/record/36322094

#include <bits/stdc++.h>

using namespace std;

int main() {
    int n, m, a[100005], minn=100000, t=0;
    cin >> n >> m;
    for(int i = 1 ; i <= n ; i++) {
        cin >> a[i];
    }
    for(int i = 1 ; i <= n-m+1 ; i++) {
        for(int j = 1 ; j <= m ; j++) {
            t += a[i+j-1];
        }
        minn = min(t, minn);
        t = 0;
    }
    cout << minn << endl;
    return 0;
}