Tình giai thừa trong Pascal (n!)

program tinhgiaithu;  uses crt;   var n,i: integer;         gt: longint; begin   write('Giai thua cua n='); readln(n);     gt:=1;   if N<0 then writeln(#7,'Khong duoc vi N<0')     else    begin       if N>0 then      for i:=1 to N do gt:=gt*i;     writeln(N,'!=',gt);    end;   readln end.