#include "bits/stdc++.h"

using namespace std;

const char en = '\n';
using  ll =          long long;
using ull = unsigned long long;


int main(){
	ios::sync_with_stdio(false);cin.tie();
	int in;

	for(int i=1;i<=9;i++){
		cin>>in;
		if(in!=i){
			cout<<i<<en;
			return 0;
		}
	}
	cout<<10<<en;

	return 0;
}