#include<bits/stdc++.h>
using namespace std;
const int maxsize=100001;
int a[maxsize];
vector<int>v;
int main()
{
int n;
memset(a,0,sizeof(a));
cin>>n;
for(int i=0;i<n;++i)
{
int num;
cin>>num;
a[num]++;
v.push_back(num);
}
int f=1;
for(int i=0;i<v.size();++i)
{
if(a[v[i]]==1)
{
f=0;
cout<<v[i];
break;
}
}
if(f==1)
cout<<"None";
}
水题
找第一个独一无二的树