#include<cstdio>

#include<cstring>

#include<cmath>

#include<vector>

#include<map>

#include<queue>

#include<stack>

#include<string>

#include<algorithm>

using namespace std;

int n;

int a[+];

int f[+];

int main()

{

    memset(f,,sizeof f);

    scanf("%d",&n);

    for(int i=;i<=n;i++) scanf("%d",&a[i]);

    for(int i=;i<=n;i++) f[a[i]]++;

    int fail=;

    for(int i=;i<=n;i++)

    {

        if(f[a[i]]==)

        {

            fail=;

            printf("%d\n",a[i]);

            break;

        }

    }

    if(fail==) printf("None\n");

    return ;

}