#include <stdio.h>
int main()
{
    int n;
    int m;
    scanf("%d%d", &n,&m);
    int arr[3000];
    for (int i = 0; i < n; i++)
    {
        scanf("%d", &arr[i]);
    }
    int sum[1001];
    for (int i = 0; i < n - m; i++)
    {
        sum[i] = 0;
        for (int j = 0; j < m; j++)
        {
            sum[i] = sum[i]+arr[i + j];
        }
    }
    int min = sum[0];
    for (int i = 1; i < n - m; i++)
    {
        if (sum[i] < min)
        {
            min = sum[i];
        }
    }
    printf("%d", min);
    return 0;
}