#include <iostream>
#include <cstring>
#include <algorithm>

using namespace std;

int main()
{
    int T;
    cin >> T;
    while (T -- )
    {
        int n, d;
        cin >> n >> d;
        int res = 0;
        for (int i = 0; i < n; i ++ )
        {
            int x;
            cin >> x;
            if (!i) res += x;
            else
            {
                int t = min(x, d / i);
                res += t;
                d -= t * i;
            }
        }
        cout << res << endl;
    }

    return 0；
}