$_=<>;chomp;
s/A/12/g;
s/B/13/g;
s/C/14/g;
s/D/15/g;
s/E/16/g;
s/F/17/g;
for $i(split//) {$h{$i}++;}
$max = 0;
for $i(keys %h){ $max=$h{$_}if$max<$h{$_};}
for $i(sort keys %h){push @ans, $i if$max==$h{$_};}
print join " ",@ans,$/;