#include<bits/stdc++.h>
using namespace std;
#define int long long
const int N = 1e6+100;
int n,k,a[N],pre[N];
signed main(){
	cin>>n>>k;
	for(int i=1;i<n;i++){
		cin>>a[i];
		pre[i+1]=pre[i]+a[i];
	}
	int ans=0x3fffffffffffffff;
	for(int i=1;i<=n;i++){
		ans=min(ans,pre[i]+pre[n]-pre[i+k]);
	} 
	cout<<ans;
	return 0;
}