#include <iostream>
#include <unordered_map>
using namespace std;
unordered_map<int,int> mp;
int a[100010];
int main()
{
int n;
cin >> n;
for(int i = 0;i < n;i ++)
{
cin >> a[i];
mp[a[i]] ++;
}
int flag = 0;
for(int i = 0;i < n;i ++)
{
if(mp[a[i]] == 1)
{
cout << a[i] << endl;
flag = 1;
break;
}
}
if(!flag) cout << "None" << endl;
return 0;
}