#include <bits/stdc++.h>
using namespace std;
int N, D, a[105], ans;
int main() {
  int T;
  cin >> T;
  while (T--) {
    cin >> N >> D;
    for (int i = 1; i <= N; i++) cin >> a[i];
    for (int i = 2; i <= N; i++) {
      int move = min(a[i], D / (i - 1));
      a[1] += move;
      D -= move * (i - 1);
    }
    cout << a[1] << endl;
  }
}
