package yukiCoder;

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;

public class No00481 {

	public static void main(String[] args) {
		BufferedReader bufferedReader = new BufferedReader(new InputStreamReader(System.in));
		String[] input = new String[9];

		try {
			input = bufferedReader.readLine().split(" ");
			for(int i = 1; i < 11 ; i++) {
				if (Integer.parseInt(input[i-1]) != i) {
					System.out.println(i);
					break;
				}
			}
		} catch (IOException e) {
			e.printStackTrace();
		}
	}
}