PAT A 1041

#include<cstdio>
using namespace std;
int vis[100005] = {0};
int num[100005] = {0};
int main()
{
    int n,i;
    scanf("%d",&n);
    for(i = 0; i<n; ++i)
    {
        scanf("%d",(num+i));
        vis[*(num+i)]++;
    }
    for(i = 0; i<n; ++i)
        if(vis[*(num+i)]==1)
            break;
    if(i==n)
        puts("None");
    else
        printf("%d\n",*(num+i));
    return 0;
}