#include <iostream>
using namespace std;

int main()
{
    int array[9];
    
    for (int i = 0; i < 9; ++i) {
        cin >> array[i];
    }
    
    bool b = true;
    
    for (int i = 0; i < 9; ++i) {
        if (array[i] != i + 1) {
            cout << i + 1 << endl;
            b = false;
            break;
        }
    }
    
    if (b) {
        cout << 10 << endl;
    }
    
    return 0;
    
}