#include <bits/stdc++.h>

using namespace std;
int a[3001] = {0};
int _min = 999999;

int main() {
    ios::sync_with_stdio(false); //读入输出优化的强迫症
    int n, m;
    cin >> n >> m;
    for (int i = 1; i <= n; i++) {
        cin >> a[i];
    }

    for (int i = 1; i <= n - m + 1; i++) {
        int sum = 0;
        for (int j = 1; j <= m; j++) {
            sum += a[i + j-1];
        }
        if (_min > sum) _min = sum;
    }
    cout << _min << endl;
    return 0;
}