#include <iostream>
#include <vector>
using namespace std;

int findMissingNumber(vector<int>& arr) {

    if (arr[0] != 1)
        return 1;

    for (int i = 0; i < arr.size() - 1; i++) {
        if (arr[i + 1] - arr[i] > 1) {
            return arr[i] + 1;
        }
    }


    return 10;
}

int main() {
    vector<int> arr(9);
    for (int i = 0; i < 9; i++) {
        cin >> arr[i];
    }

    cout << findMissingNumber(arr) << endl;
    return 0;
}