using System;

public class Program {
	public static void Main(string[] args) {
		string[] s = Console.ReadLine().Split(' ');
		for (int i = 0; i < 10; i++) {
			if (i == 9) {
				Console.WriteLine("10");
				break;
			} else if (int.Parse(s[i]) != i + 1) {
				Console.WriteLine(i + 1);
				break;
			}
		}
	}
}