#include<iostream>
using namespace std;
int main()
{
    int B[9];
    for(int i = 0; i < 9; i++)
    {
        cin >> B[i];
        if(B[i] != i + 1)
        {
            cout << i + 1 << endl;
            return 0;
        }
    }
    cout << 10 << endl;
    return 0;
}