#include <algorithm>
#include <iostream>
#include <iomanip>
#include <climits>
#include <string>
#include <vector>
#include <cmath>
#include <set>
#include <map>
using namespace std;
using ll = long long;

int main(void)
{
  map<int, int> B;
  for (int i = 0; i < 9; i++)
  {
    int temp;
    cin >> temp;
    B[temp]++;
  }
  for (int i = 1; i <= 10; i++)
  {
    if (B.find(i) == B.end())
    {
      cout << i << endl;
      break;
    }
  }

  return 0;
}