#!/usr/bin/perl

use warnings; use strict;

sub find_nth {
   my ($s,$c,$n) = @_;
   my $pos = -1;
   while ($n--) {
      $pos = index($s,$c,$pos+1);
      return -1 if $pos == -1;
   }
   return $pos;
}

my $str="Now is the time for all good men to come to the aid of their country";
my $n = 5;
my $c = "o";

print find_nth($str,$c,$n), "\n";