use warnings;
use strict;

open (IN, "in.txt") or die;
open (OUT, ">out.txt") or die;

my $previous_line = <IN>;

while (my $current_line = <IN>) {
	chomp for ($previous_line, $current_line);
	unless ( ($current_line =~ /^s/) and ($previous_line =~ /^s/) ) {
		print OUT "$current_line\n";
	}
}

close IN;
close OUT;