program Factorial;
function Factorial(n: Integer): LongInt;
begin
if n = 0 then
Factorial := 1
else
Factorial := n * Factorial(n - 1);
end;
var
num: Integer;
begin
num := 6;
WriteLn('Factorial of ', num, ' = ', Factorial(num));
end.
(*
run:
Factorial of 6 = 720
*)