using System;
using System.Linq;
using Internal;
using System.Collections.Generic;
using System.Text;

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 long NextLong()
    {
        return long.Parse(Next());
    }

    public double NextDouble()
    {
        return double.Parse(Next());
    }

    public ulong NextUlong()
    {
        return ulong.Parse(Next());
    }

    public decimal NextDecimal()
    {
        return decimal.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 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;
    }

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

class Program
{
    static bool IsPrime(long n) {
        if (n < 2) {
            return false;
        }
        for (long i = 2; i <= Math.Sqrt(n); i++) {
            if (n % i == 0) {
                return false;
            }
        }
        return true;
    }

    static void Main()
    {
        Scanner sc = new Scanner();
        long N = sc.NextLong();
        long K = sc.NextLong();
        long count = 0;
        for (long i = 1; i <= N; i++)
        {
            for (long j = i + 1; j <= N; j++)
            {
                if (IsPrime(i) && IsPrime(j) && i != j)
                {
                    count++;
                    if (count == K)
                    {
                        Console.WriteLine("{0}/{1}", i, j);
                        return;
                    }
                }
            }
        }
        Console.WriteLine("-1");
    }
}