#include <bits/stdc++.h>
using namespace std;
#define REP(i,N) for(i=0;i<N;i++)
typedef long long ll;
typedef pair<int, int> P;
typedef struct{
  int first;
  int second;
  int third;
}T;

//昇順
bool comp_Se(T& l, T& r){
  return l.second < r.second;
}

int main(void){
  vector<bool>f(10,true);
  int i,x;
  REP(i,9){
    cin >> x;
    f[x-1] = false;
  }
  REP(i,10){
    if(f[i]) cout << i+1 << endl;
  }
  return 0;
}