I use Borland 3.1. Therefore, I can't get large storage as in
FreePascal. Example:

a: array[1...100000] of longint in Free Pascal.
But

long a[1000000];
It's  impossible.

Someone advised me to use model "Large". But I don't know how to use
it and what it is.

Hi, My Name :)...Why don't you use Visual C++? Although if you don't
like it make:
const max = 100;
long a[max];
...
....
...
And when you submit your problem just nake max=100000...their
compiler will compile your program correct and if it is right you
will get Accepted....