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"); } } }