using System; using System.Collections.Generic; using System.Linq; using System.IO; using SB = System.Text.StringBuilder; //using System.Threading.Tasks; //using System.Text.RegularExpressions; //using System.Globalization; //using System.Diagnostics; using static System.Console; using System.Numerics; using static System.Math; using pair = Pair; class Program { static void Main() { //SetOut(new StreamWriter(OpenStandardOutput()) { AutoFlush = false }); new Program().solve(); Out.Flush(); } readonly Scanner cin = new Scanner(); readonly int[] dd = { 0, 1, 0, -1, 0 }; //→↓←↑ readonly int mod = 1000000007; readonly int dom = 998244353; bool chmax(ref T a, T b) where T : IComparable { if (a.CompareTo(b) < 0) { a = b; return true; } return false; } bool chmin(ref T a, T b) where T : IComparable { if (b.CompareTo(a) < 0) { a = b; return true; } return false; } bool check(long A, long B, long C) { return (A + B) % C == 0 && (A + C) % B == 0 && (C + B) % A == 0; } void solve() { var A = cin.nextlong; var B = cin.nextlong; var K = A + B; var L = new SortedSet(); for (long i = 1; i * i <= K; i++) { if (K % i == 0) { L.Add(i); L.Add(K / i); } } foreach (var i in L) { if (check(A, B, i)) { WriteLine(i); return; } } WriteLine(-1); } } static class Ex { public static void join(this IEnumerable values, string sep = " ") => WriteLine(string.Join(sep, values)); public static string concat(this IEnumerable values) => string.Concat(values); public static string reverse(this string s) { var t = s.ToCharArray(); Array.Reverse(t); return t.concat(); } public static int lower_bound(this IList arr, T val) where T : IComparable { int low = 0, high = arr.Count; int mid; while (low < high) { mid = ((high - low) >> 1) + low; if (arr[mid].CompareTo(val) < 0) low = mid + 1; else high = mid; } return low; } public static int upper_bound(this IList arr, T val) where T : IComparable { int low = 0, high = arr.Count; int mid; while (low < high) { mid = ((high - low) >> 1) + low; if (arr[mid].CompareTo(val) <= 0) low = mid + 1; else high = mid; } return low; } } class Pair : IComparable> where T : IComparable where U : IComparable { public T f; public U s; public Pair(T f, U s) { this.f = f; this.s = s; } public int CompareTo(Pair a) => f.CompareTo(a.f) != 0 ? f.CompareTo(a.f) : s.CompareTo(a.s); public override string ToString() => $"{f} {s}"; } class Scanner { string[] s; int i; readonly char[] cs = new char[] { ' ' }; public Scanner() { s = new string[0]; i = 0; } public string[] scan => ReadLine().Split(); public int[] scanint => Array.ConvertAll(scan, int.Parse); public long[] scanlong => Array.ConvertAll(scan, long.Parse); public double[] scandouble => Array.ConvertAll(scan, double.Parse); public string next { get { if (i < s.Length) return s[i++]; string st = ReadLine(); while (st == "") st = ReadLine(); s = st.Split(cs, StringSplitOptions.RemoveEmptyEntries); i = 0; return next; } } public int nextint => int.Parse(next); public long nextlong => long.Parse(next); public double nextdouble => double.Parse(next); }