#include <bits/stdc++.h>
using namespace std;
long long n, m, imp;
long long a, b[1000005];

int main() {
	ios::sync_with_stdio(false);
	imp = -INT_MAX;
	cin >> n >> m;
	if (m >= n) {
		cout << 0;
		return 0;
	}
	for (int i = 1; i < n; i++) {
		cin >> a;
		b[i] = b[i - 1] + a;
	}
	for (int i = 1; i < n - m; i++) {
		imp = max(imp, b[i + m - 1] - b[i - 1]);
	}
	cout << b[n - 1] - imp;

	return 0;
}

WA on #2 #17