#include <bits/stdc++.h>
#include <cstring>
#define INF 0x7f7f7f7f
#define eps 1e-6
#define ll long long
#define ull unsigned long long
#define N 1000010
#define _rep(i,a,b) for(int (i)=(a);(i)<=(b);(i)++)
#define rint register int
using namespace std;
ll n,k;
ll a[N],f[N];
ll ans = INF;
int main()
{
//	std::ios::sync_with_stdio(false);
	cin>>n>>k;
	if(k >= n - 1)
	{
		printf("0");
		return 0;
	}
	for(rint i=1;i<n;i++)
	{
		int x; cin>>x; f[i] = f[i-1] + x;
	}
	ll now = f[k];
	for(rint i=2;i<=n-k;++i)
	{
		now = max(now,f[i+k-1] - f[i-1]);
	}
	cout<<f[n-1] - now;
	return 0;
}