#include<bits/stdc++.h>
using namespace std;
int a[100005],ans[100005];
int main(){
	int n,m;
	cin>>n>>m;
	int answer=0;
	for(register int i=1;i<n;++i){
	    cin>>a[i];
	    answer+=a[i];
	}
	if(m==0){
	    cout<<answer<<endl;
	    return 0;
	}
	for(int i=1;i<=m;i++) ans[1]+=a[i];
	for(register int i=2;i<=n-m;++i){
		ans[i]=ans[i-1]-a[i-1]+a[i+m-1];
	}
	int big=0;
	for(int i=1;i<=n-m+1;i++) if(ans[i]>big) big=ans[i];
	answer-=big;
	cout<<answer<<endl;
return 0;
}