var a:array['a'..'z'] of longint;
var s:ansistring;
var ans,i,j:longint;
begin
  readln(s);for i:=1 to length(s) do inc(a[s[i]]);
  for i:=1 to 26 do if a[chr(i+ord('a'))] mod 2=1 then inc(ans);
  if ans=0 then inc(ans);writeln(ans);
end.