#include <bits/stdc++.h>
#include <fstream>
#include <limits.h>
#define INF (1e9) + 7;
using namespace std;
ifstream f("progresie.in");
ofstream g("progresie.out");

int fact[1000001], lastFact = 1;

int main()
{

    int t;
    f >> t;

    for (int z = 1; z <= t; z++)
    {
        int n, r;

        f >> n >> r;

        int eStart = (n - 1) * r + 1;

        int cr = r;

        //eStart * (eStart - 1) + 1
        //eStart * eStart

        int c = eStart * (eStart - 1) + 1;

        while (c <= eStart * eStart)
        {
            c += r;
            n--;
        }

    if (n==0)
        g << eStart * (eStart - 1) + 1;
    else g << -1;
    g<<endl;

    }

    return 0;
}