program chuso_max;
const f1='CHUSO_MAX.INP';
f2='CHUSO_MAX.OUT';
var f,g:text;
n,max,so:longint;
begin
Assign(f,f1); reset(f);
Assign(g,f2); rewrite(g);
readln(f,n);
max:=0;
while n>0 do
begin
so:=n mod 10;
if so>max then max:=so;
n:=n div 10;
end;
write(g,max);
close(f); close(g);
end.