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.

program bai_giai;
var f,g:text;
    A:array[1..10000] of longint;
    n,i,max:longint;
begin
    Assign(f,'Dulieu.txt');  reset(f);
    Assign(g,'BT.txt');  rewrite(g);
    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);
end.