#include <bits/stdc++.h>
#define rep(i, n) for (int i = 0; i < (n); i++)
using namespace std;
using ll = long long;
using pii = pair<int, int>;

int main() {
  vector<int> v(10);
  rep(i, 9) {
    int b;
    cin >> b;
    v[b - 1] = 1;
  }
  rep(i, 10) {
    if (v[i] == 0) {
      cout << i + 1 << endl;
      break;
    }
  }
  return 0;
}