using System;
using System.Collections;
using System.Collections.Generic;
using System.Linq;
using System.IO;
using System.Text;
using System.Globalization;
using System.Diagnostics;

namespace atcoder
{
    class Solver
    {
        public Solver() { }

        public static int Main()
        {
            new Solver().Solve();
            return 0;
        }

        Scanner cin;

        public void Solve2()
        {
            cin = new Scanner();
            string S = cin.next();

            char[] c = S.ToCharArray();

            List<char> l = new List<char>();

            int n = 0;
            for (int i = 0; i < S.Length; i++)
            {
                if (l.Count == 0 || c[i] == l[l.Count - 1]) { l.Add(c[i]); }
                else
                {
                    n = n + 2;
                }
            }

            Console.Write(n);
        }

        Boolean Stack()
        {
            return true;
        }

        public void Solve()
        {
            cin = new Scanner();
            int A = cin.nextInt();
            int B = cin.nextInt();
            int K = cin.nextInt();

            List<int> l = new List<int>();

            for (int i = 1; i <= A; i++)
            {
                if (A % i == 0)
                {
                    l.Add(i);
                }
            }

            for (int j = 0; j < l.Count; j++)
            {
                if (B % l[j] != 0)
                {
                    l.RemoveAt(j);
                    j--;
                }
            }

            Console.Write(l[l.Count-K]);
        }
    }

    class Scanner
    {
        string[] s;
        int i;

        char[] cs = new char[] { ' ' };

        public Scanner()
        {
            s = new string[0];
            i = 0;
        }

        public string next()
        {
            if (i < s.Length) return s[i++];
            string st = Console.ReadLine();
            while (st == "") st = Console.ReadLine();
            s = st.Split(cs, StringSplitOptions.RemoveEmptyEntries);
            if (s.Length == 0) return next();
            i = 0;
            return s[i++];
        }

        public int nextInt()
        {
            return int.Parse(next());
        }

        public int[] ArrayInt(int N, int add = 0)
        {
            int[] Array = new int[N];
            for (int i = 0; i < N; i++)
            {
                Array[i] = nextInt() + add;
            }
            return Array;
        }

        public long nextLong()
        {
            return long.Parse(next());
        }

        public long[] ArrayLong(int N, long add = 0)
        {
            long[] Array = new long[N];
            for (int i = 0; i < N; i++)
            {
                Array[i] = nextLong() + add;
            }
            return Array;
        }

        public double nextDouble()
        {
            return double.Parse(next());
        }

        public double[] ArrayDouble(int N, double add = 0)
        {
            double[] Array = new double[N];
            for (int i = 0; i < N; i++)
            {
                Array[i] = nextDouble() + add;
            }
            return Array;
        }
    }
}

Measured memory_bytes: 11092