#include<iostream>
#include<algorithm>
#include<cstring>
#include<unordered_map>

using namespace std;

const int N = 100010;

int n;
int a[N];

int main()
{
    cin>>n;
    unordered_map<int,int> mp;
    for(int i = 0; i<n; i++)
    {
        cin>>a[i];
        mp[a[i]]++;
    }
    for(int i = 0; i<n; i++)
        if(mp[a[i]] == 1)
        {
            cout<<a[i];
            return 0;
        }
    cout<<"None";
    return 0;
}