#include<iostream>
using namespace std;
#include<cmath>



int main()
{
	int n, m;
	cin >> n >> m;
	int* a = new int[n];
	for (int i = 0; i < n; i++)
	{
		cin >> a[i];
	}
	int num = 3000;
	int x = 0;
	for (int i = 0; i < n - m + 1; i++)
	{
		for (int j = i; j < i + m; j++)
		{
			x = a[j] + x;
		}
		num = min(num, x);
		x = 0;
	}
	cout << num << endl;


	delete[] a;
	system("pause");
	return 0;
}