#include <stdio.h>
#include <limits.h>

int main() {
    int m, n; 
    int arr[1000] = { 0 };
    scanf("%d %d", &m, &n);
    for (int i = 0;i < m;i++) scanf("%d", &arr[i]);
    int c = 0, min = INT_MAX;
    for (int i = 0;i < n;i++) {
        c += arr[i];
    }
    min = c;
    for (int i = 1;i <= m - n;i++) {
        c = c - arr[i - 1] + arr[i + n-1];
        if (c < min) {
            min = c;
        }
    }
    printf("%d", min);
}