#include <bits/stdc++.h>
using namespace std;
int main()
{
	long long n,m,ans=0,s[11000001],cnt=0,t=0,df; cin>>n>>m;
	n-=1;
	m+=1;
	s[0]=0;
	s[n+1]=1e15;
	for(int i=1;i<=n;i++)
	{
		cin>>df;
		s[i]=s[i-1]+df;
		t+=df;
	}
	for(int i=1;i<=n-m+1;i++)
	{
		ans=max(ans,s[i+m-1]-s[i]);
		//cout<<ans<<endl;
	 } 
	 if(m==-1) cout<<t; 
	 else if(m==n+2) cout<<0;
	 else cout<<t-ans;
	return 0;
}