#include<iostream>
#include<vector>
#include<algorithm>
#include<string>
#include<cmath>
#include<climits>
#include<map>
#include<set>
#include<queue>
#include<stack>
#include<bitset>
#include<iomanip>
#include<functional>
using namespace std;

#define YES cout << "YES\n"
#define Yes cout << "Yes\n"
#define yes cout << "yes\n"
#define NO cout << "NO\n"
#define No cout << "No\n"
#define no cout << "no\n"
#define rep(i,j,n) for(int i=(j);i<(n);i++)
#define erep(i,j,n) for(int i=(j);i<=(n);i++)
#define all(i) i.begin(),i.end()
#define rall(i) i.rbegin(),i.rend()
#define INF 1e9
const int mod = 1e9+7;

typedef vector<int> vi;
typedef vector<vector<int>> vvi;
typedef vector<string> vs;
typedef vector<vector<string>> vvs;
typedef pair<int, int> pi;
typedef long long i64;

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