#include <cmath>
#include <cstdio>
#include <vector>
#include <iostream>
#include <algorithm>
using namespace std;


int main() 
{
    int q;
    cin>>q;
    while(q--)
    {
        int len,c;
        cin>>len>>c;
        if(c>(len*(len-1)/2))
            cout<<"-1\n";
    }
    /* Enter your code here. Read input from STDIN. Print output to STDOUT */   
    return 0;
}