#include <bits/stdc++.h>

using namespace std;
const int N = 3010;
int a[N];
int MIN;

int main() {
    //滑动窗口思想
    int n, m;
    cin >> n >> m;
    for (int i = 1; i <= n; i++) cin >> a[i];

    //第一组m个数
    int sum = 0;
    for (int i = 1; i <= m; i++) sum += a[i];
    MIN = sum;//第一组数的和是默认值

    //滑动窗口,加入下一个数字，减去顶部的数字
    for (int i = m + 1; i <= n; i++) {
        sum = sum + a[i] - a[i - m];
        //不断的取min,找出和的最小值
        MIN = min(MIN, sum);
    }
    //输出最小值
    printf("%d", MIN);
    return 0;
}