#include<bits/stdc++.h>
#define int long long
using namespace std;
int n,k,arr[1000050],mx,tmp,sum;
signed main()
{
	cin>>n>>k;
	for(int i=1;i<=n-1;i++)
	{
		cin>>arr[i];
		sum+=arr[i];
	}
	for(int i=1;i<=min(n,k);i++)
	{
		tmp+=arr[i];
	}
	mx=tmp;
	for(int i=k+1;i<=n-1;i++)
	{
		tmp-=arr[i-k];
		tmp+=arr[i];
		mx=max(mx,tmp);
	}
	cout<<sum-tmp<<endl;
	return 0;
}

https://www.luogu.com.cn/record/173553249