import java.util.*;

public class Main {
  public static void main(String[] args) {
    Scanner sc = new Scanner(System.in);
    int ans = 10;
    for(int i = 1; i <= 9; i++) {
      if(i != sc.nextInt()) {
        ans = i;
        break;
      }
    }
    System.out.println(ans);
  }
}