#include<bits/stdc++.h>
#define ll long long
#define ull unsigned long long
#define fr first
#define se second
#define FAST ios::sync_with_stdio(false), cin.tie(0), cout.tie(0)
using namespace std;
int n,k;
ll pre[1000005],a[1000005],maxn;
int main(){
	FAST;
	cin>>n>>k;
	for(int i=1;i<n;i++){
		cin>>a[i];
		pre[i]=pre[i-1]+a[i];
	}
	for(int i=1;i<n;i++){
		maxn=max(maxn,pre[i]-pre[i-k]);
	}
	cout<<pre[n-1]-maxn;
	return 0;
}