#include <bits/stdc++.h>
using namespace std;
const int N = 1e6 + 5;
long long a[N], sum[N], n, k, maxi=-1e18;
int main()
{
	cin >> n >> k;
	for(int i = 1;i <= n-1;i ++)
	{
		cin >> a[i];
		sum[i] = sum[i-1] + a[i];
	}
	for(int i = 1; i + k-1 <= n-1;i ++)
	{
		maxi = max (maxi, sum[i + k-1] - sum[i-1]);
	}
	cout << sum[n-1] - maxi << endl;
	return 0;
} 

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