#include<iostream>
#include<vector>
#include<cmath>
#include<iomanip>
#include <sstream>
#include<algorithm>
int s[20000];
int main() {
    int m, n;
    std::cin >> m >> n;
    std::vector<int>v;
    int min=301;
    for (int i = 0; i < m; i++) {
        int x;
        std::cin >> x;
        v.push_back(x);
        if (i >= n-1) {
            int sum =0;
            for (int j = 0; j < n; j++)
                sum += v[i - j];
            if (sum < min)
                min = sum;
        }
    }
    if (m == 0||n==0)
        std::cout << 0;
    else
        std::cout << min;
}