#include<bits/stdc++.h>
using namespace std;
long long n, a[100000000], minn = 1000000000000000000, m;
int main() {
	cin >> n >> m;
	for (int i = 1; i <= n; i++) {
		cin >> a[i];
	}
	for (int i = 1; i <= n - m; i++) {
		int ans = 0;
		for (int j = i; j <= m + i - 1; j++) {
			ans += a[j];
		}
		if (ans < minn)minn = ans;
	}
	cout << minn;
	return 0;
}