#include <bits/stdc++.h>
using namespace std;
void solve_by_payel(int n, int samp[])
{
    int reslt = 0;
    for(int i = 0; i < n; i++)
    {
        int flag = 0;  
        for(int j = 0; j < n; j++)
        {
            if(i != j && samp[i] == samp[j])
            {
                flag = 1;
                break;
            }
        }
        
        if(flag == 0)
        {
            reslt = samp[i];
            break;  
        }
    }
    cout << reslt << endl;
}

int main()
{
    int n;
    cin >> n;
    int samp[n];
    for(int i = 0; i < n; i++)
    {
        cin >> samp[i];
    }
    solve_by_payel(n, samp);

    return 0;
}