#include <iostream>
using namespace std;
int a[10];

int main() {
  int n;
  for (size_t i = 0; i < 9; i++) {
    cin >> n;
    a[n-1]++;
  }
  for (size_t i = 0; i < 10; i++) {
    if (a[i] == 0) {
      cout << i + 1 << endl;
      break;
    }
  }
}