/* Solved by Sakhawat Hossain Mahin, CSE-28th, SMUCT */
#include<bits/stdc++.h>
using namespace std;
#define endl '\n'
#define int long long
#define fastIO ios_base::sync_with_stdio(false), cin.tie(nullptr), cout.tie(nullptr);

int32_t main()
{
    fastIO

    int n;
    cin>>n;
    map<int,int>mp;

    for(int i = 0; i<n; i++){
        int x;
        cin>>x;
        mp[x]++;
    }   

    for(auto i : mp){
        if(i.second == 1){
            cout << i.first << endl;
            break;
        }
    }

    return 0;
}