namespace AtCoder;

#nullable enable

using System.Numerics;

static class Extensions
{
    public static T[] Repeat<T>(this int time, Func<T> F) => Enumerable.Range(0, time).Select(_ => F()).ToArray();
}

class AtCoder
{
    object? Solve()
    {
        var t = Int();
        var ans = t.Repeat(() => -1L);
        for (var l = 0; l < t; l++)
        {
            var a = Int();
            var b = Int();
            var d = b - a;
            var lns = long.MaxValue;
            if (b % a == 0) lns = 0;
            for (var i = 1L; i * i <= d; i++)
            {
                if (d % i != 0) continue;
                var x = i - a;
                if (x > 0) lns = Math.Min(lns, x);
                var j = d / i;
                x = j - a;
                if (x > 0) lns = Math.Min(lns, x);
            }
            ans[l] = lns == long.MaxValue ? -1 : lns;
        }
        Out(ans);
        return null;
    }

    public static void Main() => new AtCoder().Run();
    public void Run()
    {
        var res = Solve();
        if (res != null)
        {
            if (res is bool yes) res = yes ? "Yes" : "No";
            sw.WriteLine(res);
        }
        sw.Flush();
    }

    string[] input = Array.Empty<string>();
    int iter = 0;
    readonly StreamWriter sw = new(Console.OpenStandardOutput()) { AutoFlush = false };

    string String()
    {
        while (iter >= input.Length) (input, iter) = (Console.ReadLine()!.Split(' '), 0);
        return input[iter++];
    }
    T Input<T>() where T : IParsable<T> => T.Parse(String(), null);
    int Int() => Input<int>();
    void Out(object? x, string? separator = null)
    {
        separator ??= Environment.NewLine;
        if (x is System.Collections.IEnumerable obj and not string)
        {
            var firstLine = true;
            foreach (var item in obj)
            {
                if (!firstLine) sw.Write(separator);
                firstLine = false;
                sw.Write(item);
            }
        }
        else sw.Write(x);
        sw.WriteLine();
    }
}