#include <bits/stdc++.h>
#define rep(i, ss, ee) for (int i = ss; i < ee; ++i)
using namespace std;

int main() {
  vector<bool> v(11, true);
  v[0] = false;
  int x;
  rep(i, 0, 9) {
    cin >> x;
    v[x] = false;
  }
  rep(i,1,11){
    if (v[i]) {
      cout << i << endl;
      break;
    }
  }
  getchar();
}