use strict;
use warnings;

use File::Find::Rule qw( );

my %files;
for (
   File::Find::Rule
      ->file()
      ->name('*.rtf', '*.ftp')
      ->in('.')
) {
   my ($name) = /^(.*)\./;
   ++$files_by_ext{$name};
}

say for grep {$files{$_} == 2} keys %files;