// Online C++ compiler to run C++ program online
#include <iostream>
#include "unordered_map"
#include "algorithm"
using namespace std;

int main() {
    ios :: sync_with_stdio(false);
    cin.tie(0);
    
    int tc = 1;
    //cin>>tc;
    while(tc--){
        int n;
        cin>>n;
        unordered_map<int,int>ump;
        for(int i=0;i<n;i++){
            int it;
            cin>>it;
            ump[it]++;
        }
        for(auto it:ump){
            if(it.second == 1){
                cout<<it.first<<endl;
                break;
            }
        }
    }

    return 0;
}