using System;
using System.Collections.Generic;
using System.Linq;

public class MyLib {
    public static List<int> GetIntListFromTextReader(System.IO.TextReader reader, char delimitor) {
        return reader.ReadLine().Split( delimitor ).ToList<string>().ConvertAll<int>( int.Parse );
    }
    public static void WriteTextStream(System.IO.TextWriter writer, object args) {
        writer.WriteLine( args );
    }
}

public class Program {
    public static int Solver(System.IO.TextReader input) {
        var remains = Enumerable.Range( 1, 10 ).ToList<int>();
        var b = MyLib.GetIntListFromTextReader( input, ' ' );
        foreach (var n in b) {
            remains.Remove( n );
        }
        return remains.ElementAt( 0 );
    }

    private static void Main() {
        Console.WriteLine( Solver( Console.In ) );
    }
}