#include <iostream>
#include <stdio.h>
using namespace std;

int main(int argc, char const* argv[])
{
    int n[9];
    for (int i = 0; i < 9; i++) {
        cin>>n[i];
    }
    int ans;
    for (int i = 0; i < 9; i++) {
        if(n[i]!=i+1){
            ans=i+1;
            cout<<ans<<endl;
            return 0;
        }
    }
    cout<<"10"<<endl;
    return 0;
}