using System;
using System.Linq;

public class P0481 {
    public static void Main() {
        var a = Console.ReadLine().Trim().Split(' ').Select(int.Parse).ToList();
        a.Add(0);
        Console.WriteLine(Enumerable.Range(1, 10).Zip(a, (i, j) =>  new { left = i, right = j }).First(pair => pair.left != pair.right).left);
    }
}