use strict;

$| = 1;  # turn off output buffering

if ( @ARGV and $ARGV[0] =~ /^\d+$/ and ! -f $ARGV[0] ) {
   show_sec( @ARGV );
} 
else {
   while (<>) # read a line from STDIN (or from a named file)
   {
      chomp;
      show_sec( $_ );
   }
}

sub show_sec
{
   for ( @_ ) {
      if (/^\d+$/) {
         my $sec = $_ * 86400;
         my $s = ( $_ == 1 ) ? '':'s';
         print "[$_] day$s = [$sec] seconds\n";
      } else {
         warn "$_ is not a positive integer; I'll ignore that.\n";
      }
   }
}