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