import java.io.*;
import java.util.*;
import java.text.*;
import java.math.*;
import java.util.regex.*;

public class Solution {

    public static void main(String[] args) {
        Scanner in = new Scanner(System.in);
        int q = in.nextInt();
        for(int a0 = 0; a0 < q; a0++){
            int len = in.nextInt();
            int c = in.nextInt();
            // your code goes here
            
          
            int maxCompare = ((len - 1) * (len) / 2);
            // output -1 if not possible
            if(c > maxCompare) {
                System.out.println("-1");
            }
              
        }
    }
}