#include<bits/stdc++.h>
#define iamspeed ios_base::sync_with_stdio(false);cin.tie(NULL);cout.tie(NULL);
#define endl '\n'
using namespace std;
typedef long long int ll;
const ll modd=1e9+7;
const ll N=1e6+5;
ll x,y,z,n,m,k,w,sum,ans,cnt,cnt2,res,mn,mx,t,tt,q,i,j;
string s,ss;
int main()
{
    iamspeed


    cin>>n;
    vector<ll>a(n);
    map<ll,ll>mp;
    for(i=0; i<n; i++)
    {
        cin>>a[i];
        mp[a[i]]++;
    }
    for(auto [fir,sec]:mp)
    {
        if(sec==1)ans=fir;
    }
    cout<<ans<<endl;



    return 0;
}