#include <iostream>
#include <vector>
#include <map>
#include <algorithm>
using namespace std;
int main()
{
	int t;
	cin >> t;
	while (t--)
	{
		int a, b;
		cin >> a >> b;
		int tmp = b - a;
		if (tmp == 0)
		{
			cout << 0 << endl;
			continue;
		}
		int ans = 2e9;
		for (int i = 1; i * i <= tmp; ++i)
		{
			if (tmp % i == 0)
			{
				if (i >= a)
				{
					ans = min(ans, i - a);
				}
				if (tmp / i >= a)
				{
					ans = min(ans, tmp / i - a);
				}
			}
		}
		cout << (ans >= 2e9 ? -1 : ans) << endl;
	}
}