use strict;

while( <DATA> ) {
    if( /^1$/ ) {
        my $n = 0;
        ++$n while defined( $_ = <DATA> ) and /^\n$/;
        $n = 1 if /_____ 2/;
        print '1', "\n" x $n;
    }
    print;
}
__DATA__


1


b

1



_____ 2