import java.io.BufferedInputStream;
import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.util.*;

public class _481 {
	public static void main(String[] args) throws IOException {
		new _481().solve();
	}

	void solve() throws IOException {
		try (final Scanner in = new Scanner(System.in)) {
			for (int i = 1; i < 10; i++) {
				if (in.nextInt() != i) {
					System.out.println(i);
					return;
				}
			}
			System.out.println(10);
		}
	}
	
	// for debug
	static void dump(Object... o) {
		System.err.println(Arrays.deepToString(o));
	}
}