#include <bits/stdc++.h>
using namespace std;

int main() {
	int n, m, a[3010], cnt = 0, minn = 12000;
	cin >> n >> m;
	for (int i = 1; i <= n; i++) {
		cin >> a[i];

		for (int j = i; j < i + m ; j++)	{
			cnt = cnt + a[j];//计算m个值的和

		}
		if (cnt <= minn)
			minn = cnt;//比较大小

	}
	cout << minn;

	return 0;
}