#include <iostream>
#include <cstdio>
#include <algorithm>
#include <vector>
#include <functional>
#include <queue>
#include <string>
#include <cstring>
#include <numeric>
#include <cstdlib>
#include <cmath>
#include <map>
#include <unordered_map>
#include <set>
using namespace std;

typedef long long ll;

#define INF 10e17
#define rep(i,n) for(long long i=0; i<n; i++)
#define repr(i,n,m) for(long long i=m; i<n; i++)
#define END cout << endl
#define MOD 1000000007
#define pb push_back
#define sorti(x) sort(x.begin(), x.end())
#define sortd(x) sort(x.begin(), x.end(), std::greater<long long>())
#define debug(x) std::cerr << (x) << std::endl;
#define roll(x) for (auto&& itr : x) { debug(itr); }

template <class T> inline void chmax(T &ans, T t) { if (t > ans) ans = t;}
template <class T> inline void chmin(T &ans, T t) { if (t < ans) ans = t;}

int main() {
  string s1, s2, s3, s4;
  getline(cin, s1);
  getline(cin, s2);
  for (auto itr : s2) {
    if (itr == ' ') {
      cout << "\"assert\"" << endl;
      return 0;
    }
  }
   
  {
    getline(cin, s3);
    getline(cin, s4);
    ll t1 = stoll(s2), t2 = stoll(s3), t3 = stoll(s4);
    // cout << t1 << " " << t2 << " " << t3 << endl;
    ll p1 = t1 + t2, p2 = t2 + t3, p3 = t1 + t3;
    map<ll, bool> mp;
    mp[p1] = true;
    mp[p2] = true;
    mp[p3] = true;
    int cnt = 0;
    for (auto itr : mp) {
      cnt += 1;
      if (mp.size() == 2 and cnt == 1) {
        cout << itr.first << endl;
        return 0;
      } else if (mp.size() == 3 and cnt == 2) {
        cout << itr.first << endl;
        return 0;
      }
    }
  }
}