#include<iostream>
#include<math.h>
#include<cstdio>
using namespace std;
int uv[10000] = {};
int add[10000] = {};
int main() {
	int n, m;
	int minn = 0;
	cin >> n >> m;
	for (size_t i = 1; i <= n; i++) {
		cin >> uv[i];
	}
	for (size_t i = 1; i <= n - m + 1; i++) {
		for (size_t j = 0; j <= m - 1; j++) {
			add[i] += uv[i + j];
			}
	}
	for (size_t i = 1; i <= n - m + 1; i++) {
		if (i == 1) {
			minn = add[i];
		}
		minn = minn < add[i] ? minn : add[i];
	}
	printf("%d", minn);
	return 0;
}