var
t: array[0..255] of longint;
s: string;
i: longint;
begin
read(s);
for i:=0 to 255 do
t[i] := 0;
for i:=1 to length(s) do
inc(t[ord(s[i])]);
for i:=1 to length(s) do
if (t[ord(s[i])] = 1) then
begin
writeln(s[i]);
exit;
end;
writeln('no');
end. 输入：xyzxyw
输出：1
