#include<bits/stdc++.h>
using namespace std;

int main(){
	cin.tie(0),ios::sync_with_stdio(false);
	for(int i=1;i<=9;++i){
		int b; cin>>b;
		if(i!=b){
			cout<<i<<"\n"s;
			return 0;
		}
	}
	cout<<10<<"\n"s;
}