Perl Script to validate the Subnet mask

sub ValidateSubnetMask
  {
     my $ip=trim(<input>);

     if($ip=~ m/^(\d\d?\d?)\.(\d\d?\d?)\.(\d\d?\d?)\.(\d\d?\d?)\/([0-9]{1,2})$/ && ( $1 <= 255 && $2 <= 255 && $3 <= 255 && $4 <= 255 && $5 < 32))
   {   
         return 1;
       }
elsif($ip=~ m/^(\d\d?\d?)\.(\d\d?\d?)\.(\d\d?\d?)\.(\d\d?\d?)\s+(\d\d?\d?)\.(\d\d?\d?)\.(\d\d?\d?)\.(\d\d?\d?)$/ && ( $1 <= 255 && $2 <= 255 && $3 <= 255 && $4 <= 255 && $5 <= 255 && $6 <= 255 && $7 <= 255 && $8 < 255))
   {
     return 1;
   }
  else
   {
     return -1;
   }
  }