#include <bits/stdc++.h>

using namespace std;
const int N = 3010;
const int INF = 0x3f3f3f3f;
int s[N], a[N];
int n, m;
int MIN = INF;

int main() {
    cin >> n >> m;
    for (int i = 1; i <= n; i++) {
        cin >> a[i];//刺痛值
        s[i] = s[i - 1] + a[i];//构建一维前缀和
    }

    for (int i = m; i <= n; i++)
        MIN = min(MIN, s[i] - s[i - m]);//求定区间和并取最小的一部分
    //输出最小值
    printf("%d", MIN);
    return 0;
}