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();
            
            int maxC = 0;
            for (int i = 1; i < len; i++) {
                maxC += i;
            }
            
            if (c > maxC) {
                System.out.println("-1");
                continue;
            }
            
            System.out.println("0");
        }
    }
}