#include<iostream>
using namespace std;
int a[3000];
int main()
{
	int n, m;
	cin >> n >> m;
	for (int i = 0; i < n; i++)
	{
		cin >> a[i];
	}
	
	int ret = 0;
	for (int i = 0; i < n - m; i++)
	{
		int sum = 0;
		for (int j = i; j < i + m; j++)
		{
			sum += a[j];
		}
		if (i == 0) ret = sum;
		ret = min(ret, sum);
	}
	cout << ret;
	return 0;
}