#include <bits/stdc++.h>
#define int long long 
using namespace std;

signed main() {
  vector<int> A(10);
  
  int B;
  for( int i = 0; i < 9; i++ ){
    cin >> B;
    A.at(B-1)++;
  }
  for( int i = 0; i < 10; i++ ){
    if( A.at(i) == 0 ) cout << i+1 << endl;
  }
    
}