import java.util.ArrayList;
import java.util.List;
import java.util.Scanner;

public class Main {
	public static void main(String[] args) throws Exception {
		Scanner sc = new Scanner(System.in);
		int t = sc.nextInt();
		for (int z = 0; z < t; z++) {
			int a = sc.nextInt();
			int b = sc.nextInt();

			int d = b - a;
			int ans = Integer.MAX_VALUE;
			if (d % a == 0) {
				ans = 0;
			} else if (d < a) {
				ans = -1;
			} else {
				int a2 = a % d;
				List<Integer> list = divList(d);
				for (int e : list) {
					if (a2 <= e) {
						ans = Math.min(ans, e - a2);
					}
				}
			}
			System.out.println(ans);
		}
		sc.close();
	}

	static List<Integer> divList(int n) {
		List<Integer> list = new ArrayList<>();
		int end = (int) Math.sqrt(n);
		for (int i = 1; i <= end; i++) {
			if (n % i == 0) {
				list.add(i);
			}
		}
		int i = end * end == n ? list.size() - 2 : list.size() - 1;
		for ( ; i >= 0; i--) {
			list.add(n / list.get(i));
		}
		return list;
	}
}