#include <iostream>
using namespace std;
int main() {
    int n, a, b[3005], c[3005], sum = 0, min = 1000;
    cin >> n >> a;
    for (int i = 1; i <= n; i++) {
        cin >> b[i];
    }
    for (int i = 1; i <= n - 2; i++) {
        for (int j = i; j < a + i  ; j++) {
            sum += b[j];
        }
        c[i] = sum;
        sum = 0;
    }
    for (int i = 1; i <= n - 2; i++) {
        if (c[i] < min) {
            min = c[i];
        }
    }
    cout << min;
    return 0;
}