program abc; 
uses crt; 
var a,b,c,dmax : integer; 
begin 
clrscr; 
write ( ' nhap a =' ); 
readln (a); 
write ( ' nhap b = '); 
readln (b); 
write ( ' nhap c =' ); 
readln (c); 
write ( ' nhap d = ' ); 
readln (d); 
a:=max; 
if max<b then max:=b; 
if max<c then max :=c; 
if max<d then max :=d; 
write ( ' so lon nhat la',max); 
readln; 
end.