#!/usr/bin/perl -w
use strict;

my $ranking_string = "32,15,4,72,13,28,14";
my @ranking = split (/,/, $ranking_string);
my $i =1;
my %ranking_hash = map {$_ => $i++} @ranking;
my $default_best_num = (@ranking)[-1]; 

while (my $list = <DATA>) 
{
  chomp $list;
  my $best_num = $default_best_num;  
  foreach my $num (split /,/, $list)
  {
     next unless $ranking_hash{$num};
     $best_num = $num if $ranking_hash{$num} < $ranking_hash{$best_num};  
  } 
  print "$best_num\n";
}

#prints:
#15
#15
#14

__DATA__
4,13,15
4,50,15,13
50,60,70