#include<bits/stdc++.h>
using namespace std;
int n,m,a[3001],k,minn=999;
int main()
{
	cin>>n>>m;
	for(int i=1; i<=n; i++)
	{
		cin>>a[i];
	}
	for(int i=1; i<=n-m-1; i++)
	{
		k=0;
		for(int j=i; j<=m+i-1; j++)
		{
			k+=a[j];			
		}
		minn=min(minn,k);
	}
	cout<<minn;
	return 0;
}