#include <iostream>
#include <cstdio>
#include <cstring>
#include <algorithm>
using namespace std;
const int maxn = 10e+5 +10;
long long a[maxn];
int main()
{
int n;
while(~scanf("%d", &n))
{
long long tmp;
for(int i = 0; i < n; i++)
{
scanf("%lld", &a[i]);
}
sort(a, a+n);
if(a[0] != a[1])
{
printf("%d\n",a[0]);
continue;
}
if(a[n-1] != a[n-2])
{
printf("%lld\n",a[n-1]);
continue;
}
for(int i = 1; i < n-1; i++)
{
if(a[i] != a[i-1] && a[i] != a[i+1])
{
tmp = a[i];break;
}
}
printf("%lld\n",tmp);
}
return 0;
}