#include <iostream>

using namespace std;

int main()
{ long x;
  int n,z;
  cin>>n;
  long* arr = NULL;
  arr = new long[n];
  long long first_max=0;
  long long sec_max=0;

      for (int i=0; i<n; i++)
            {cin>>x;
             arr[i]=x;
             if(arr[i]>first_max)
               {
                 first_max=arr[i];
                 z=i;
               }
             }

      for (int i=0; i<n; i++)
            {
              if(arr[i]>sec_max&&i!=z)
              sec_max=arr[i];
            }

cout<<sec_max*first_max<<endl;

return 0;
}