uses crt;
var a,b,c,d,t,k:integer;
function Max(x,y:integer):boolean;
Begin
 if x>y then Max:=true else Max:=false;
End;
BEGIN
 clrscr;
 write('Nhap so thu 1: ');readln(a);
 write('Nhap so thu 2: ');readln(b);
 write('Nhap so thu 3: ');readln(c);
 write('Nhap so thu 4: ');readln(d);
 if Max(a,b) then t:=a else t:=b;
 if Max(c,d) then k:=c else k:=d;
 if Max(t,k) then write('So lon nhat la: ',t) else write('So lon nhat la: ',k);
 readln
END.

Cho mik xin hay nhất nhé mik chỉ thiếu ctlhn nữa thôi

uses crt;
var a:array[1..4] of longint;
i:byte;m1,m2:longint;
function max(x,y:longint):longint;
begin
    if x>y then exit(x);
    exit(y);
end;
begin
    clrscr;
    for i:=1 to 4 do
       begin
           write('Nhap so thu ',i,' = ');readln(a[i]);
       end;
    m1:=max(a[1],a[2]);
    m2:=max(a[3],a[4]);
    writeln('So lon nhat la: ',max(m1,m2));
readln;
end.