#include<iostream>

using namespace std;
int main()
{
	int n, m;
	int arr[5000], min=10000;
	int t = 0;
	cin >> n >> m;
	for (int i = 1; i <= n; i++)
	{
		cin >> arr[i];
	}
	for (int i = 1; i <= (n - m + 1); i++)
	{
		for (int j = i; j<m+i; j++)
		{
			t+= arr[j];
		}

		if (t < min)
		{
			min = t;

		}
		t = 0;
	}
	cout << min << endl;
}