Chắc là như vậy.
uses crt;
var f,g: text;
a: array[-500..500] of integer;
n,i:byte;
max:integer;
begin
clrscr;
assign(f,'dulieu.txt');
reset(f);
assign(g,'BT.txt');
rewrite(g);
write('N: '); readln(f,n);
for i:=1 to n do
read(f,a[i]);
max:=a[1];
for i:=2 to n do
if a[i]> max then max:=a[i];
write(g,max);
close(f);
close(g);
readln;
end.