#include <bits/stdc++.h>

using namespace std;
long long calc_max(long long n){
    int sum =0 ;
    n--;
    
    while(n!=0){
       sum = sum + n;
      n--;  
    }
    
    return sum;
    
    
    
}
int main(){
    int q;
    cin >> q;
    for(int a0 = 0; a0 < q; a0++){
        int len;
        int c;
        cin >> len >> c;
        
        if(c<len-1 || c > calc_max(len))
            cout<<"-1";// your code goes here
    }
    return 0;
}