import java.util.Scanner;
public class to {

  public static void main(String[] args){

    Scanner input = new Scanner(System.in);
    String scr = input.nextLine();

    String[]num = scr.split(" ");
    int i = 1;

    for(i = 1; i<10; i++){
      int a = Integer.parseInt(num[i-1]);//数値に変換
      if(i!=a){
        System.out.println(a-1);
        break;
      }else if(a==9){
        System.out.println("10");
      }
    }

  }

}