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

#pragma GCC optimize("Ofast")

#define rep(i,n) for(ll i=0;i<n;i++)
#define repl(i,l,r) for(ll i=(l);i<(r);i++)
#define per(i,n) for(ll i=(n)-1;i>=0;i--)
#define perl(i,r,l) for(ll i=r-1;i>=l;i--)
#define fi first
#define se second
#define pb push_back
#define ins insert
#define pqueue(x) priority_queue<x,vector<x>,greater<x>>
#define all(x) (x).begin(),(x).end()
#define CST(x) cout<<fixed<<setprecision(x)
#define rev(x) reverse(x);
using ll=long long;
using vl=vector<ll>;
using vvl=vector<vector<ll>>;
using pl=pair<ll,ll>;
using vpl=vector<pl>;
using vvpl=vector<vpl>;
const ll MOD=1000000007;
const ll MOD9=998244353;
const int inf=1e9+10;
const ll INF=4e18;
const ll dy[8]={1,0,-1,0,1,1,-1,-1};
const ll dx[8]={0,1,0,-1,1,-1,1,-1};
template <typename T> inline bool chmax(T &a, T b) {
  return ((a < b) ? (a = b, true) : (false));
}
template <typename T> inline bool chmin(T &a, T b) {
  return ((a > b) ? (a = b, true) : (false));
}


struct UnionFind {
    vector<int> par;
    vector<int> edge;
    
    UnionFind(int n) : par(n, -1),edge(n, 0) {}

    int root(int x) {
        if (par[x] < 0) return x;
        else return par[x] = root(par[x]);
    }
    
    bool same(int x, int y) {
        return root(x) == root(y);
    }
    
    bool merge(int x, int y) {
        x = root(x); y = root(y);
        if (x == y) {
            edge[x]++;
            return false;
        }
        if (par[x] > par[y]) swap(x, y);
        par[x] += par[y];
        par[y] = x;
        edge[x] += edge[y]+1;
        return true;
    }
    
    int size(int x) {
        return -par[root(x)];
    }
};


int main(){
  ios::sync_with_stdio(false);
  std::cin.tie(nullptr);
  ll p=0;rep(i,11)p^=i;
  rep(i,9){
    ll a;cin >> a;p^=a;
  }
  cout << p << endl;
}