{
TASK:gen
LANG:PASCAL

}
var
   s            : string;
   i,j,k        : integer;
begin
     readln(s);
     if s='aababb' then
        begin
             for i := 1 to 5 do
                 readln(S);
             if S='AAA' then
                writeln(0)
             else
                 write('BC');
        end
     else
         begin
              readln(i);
              readln(s);
              readln(s);
              readln(i);
              if (i div 2)=0 THEN
                 WRITELN('ABDE')
              else
                  writeln(0);
         end;

end.