import java.util.*;

class Main{
    public static void main(String args[]){
        Scanner cin = new Scanner(System.in);
        int result=0;
        int tmp;
       for(int i = 1;i<10;i++){
           tmp = cin.nextInt();
           if(i!=tmp){
               result = i;
	       if(!cin.hasNext()&&tmp==10){
                   result = 10;
               }
               break;
           }
       }
       System.out.println(result);
       }
}