#include <bits/stdc++.h>
#define ll long long
using namespace std;
const int N = 1e6 + 10;
ll a[N], f[N];
int main(){
	ll n, k; cin >> n >> k;
	for(int i = 1; i < n; i++){
		cin >> a[i];
		f[i] = f[i - 1] + a[i];
	}
	ll ans = 0;
	for(int i = 1; i < n - k; i++)
		ans = max(ans, f[i + k] - f[i]);
	cout << f[n - 1] - ans;
	return 0;
}