var
s:string;
c:set of char;
a:array[65..122] of integer;
max,i:integer;
r:char;
begin
read(s);
c:=['A'..'z'];
for i:=1 to length(s) do
if s[i] in c then
inc(a[ord(s[i])]);
max:=-1;
for i:=65 to 122 do
if(a[i]>max) then
begin
max:=a[i];
r:=chr(i);
end;
write(r);
end.