#include<iostream>
#include<algorithm>
#include<cmath>
#include<cstring>
#include<map>
#include<queue>
#include<stack>
using namespace std;
int n,m,minn = 10000;
int a[300005];
int main()
{
	cin>>n>>m;
	if(n == 0)
    {
        cout<<0;
        return 0;
    }
	for (int i = 1;i <= n;i++)
	{
		cin>>a[i];
	}
	for (int i = 1;i <= n - m + 1;i++)
	{
		int x = 0;
		for (int j = 1;j <= m;j++)
		{
			x += a[i + j - 1];
		}
		if (x < minn)
		{
			minn = x;
		}
	}
	cout<<minn;
 	return 0;
}