my $seen_16r_secmove = 0;
my $seen_17b         = 0;
my @buf;
while (<>) {
   if (/^:17B:/) {
      $seen_17b = 1;
      print @buf;
      @buf = $_;
   } elsif ($seen_16r_secmove && $seen_17b && /^:35B:/) {
      print;
   } else {
      $seen_16r_secmove = 1 if /^:16R:SECMOVE$/;
      push @buf, $_;
   }
}

print @buf;