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

#define ll long long
#define vc vector<int> 
#define pr pair<int,int>
#define PB push_back
#define MP make_pair
#define loop(i,a,b) for(int i = a; i<= b; i++)
#define YES cout<<"YES"<<endl;
#define NO cout<<"NO"<<endl;
#define bb begin()
#define ee end()
#define ff first
#define ss second
#define fastio ios::sync_with_stdio(false);cin.tie(NULL);

void solve();

int main()
{
    fastio
    int t;t=1;
    while(t--) solve();
    return 0;
}

void solve(){
    int n;cin>>n;
    map<int,int>mp;
    vc a(n);for (int i = 0; i < n; i++)
    {
        cin>>a[i];
        mp[a[i]]++;
    }
    int x;
    for(auto& it:mp){
        if(it.second==1){
            cout<<it.first<<endl;
            break;
        }
    }
    
}