#include <iostream>
using namespace std;
int main()
{
    int n, i, j, a[1000], b[1000]={0}, m, k = 0, min=0, s;
    cin >> n>>m;
    for (i = 0; i < n; i++)
    {
        cin >> a[i];
    }
    
    for (i = 0;; i++)
    {    
        s = i + m;
        if (s > n)break;//当s大于n时结束循环
        k++;
        for (j = i; j < s; j++)
        {
            b[k] = b[k] + a[j];//b数组存储所有连续m个a的和
            
        }
        
    }
    min = b[1];

    for (i = 2; i <=k; i++)//获得最小值
    {

        if (b[i] < min)min = b[i];
    }

    cout << min;
    return 0;
}