var a,b,c,d,e,max:longint;
begin
read(a);
b:=a mod 10;
if b>max then max:=b;
c:=a div 10 mod 10;
if c>max then max:=c;
d:=a div 100 mod 10;
if d>max then max:=d;
e:=a div 1000;
if e>max then max:=e;
write(max);
end.
/**************************************************************
	Problem: 1718
	User: admin
	Language: Pascal
	Result: Wrong Answer
****************************************************************/