#!/usr/bin/perl
use strict;

chomp( my @data = <DATA> );
$_ = [ split // ] for @data;

do {
  print_map(\@data);
  print "=====\n";
} while (remove_vert_seam(\@data));

sub remove_vert_seam {
    my $data = shift;
    my $seam;

    my $rows = $#$data;
    my $cols = $#{ $data[0] };
 
    for my $j (0 .. $cols) {
        $seam->[0][$j] = 0 if $data->[0][$j] eq ".";
    }

    # there is a seam from the top row to ($i,$j)
    # only if (i,j) has a "." and there is a seam from
    # the top row to any of (i-1,j-1), (i-1,j), (i-1,j+1)

    # if there is a seam, remember its predecessor so we
    # can trace it back.

    for my $i (1 .. $rows) {
    for my $j (0 .. $cols) {
        if ($data->[$i][$j] eq ".") {
            $seam->[$i][$j] = $j-1
                if $j-1 >= 0     and defined $seam->[$i-1][$j-1];
            $seam->[$i][$j] = $j
                if                   defined $seam->[$i-1][$j];
            $seam->[$i][$j] = $j+1
                if $j+1 <= $cols and defined $seam->[$i-1][$j+1];
        }
    }
    }

    # if there is a seam to the bottom row, trace it back
    # to the top and remove all of the cells that are visited

    for my $j (0 .. $cols) {
        if (defined $seam->[$rows][$j]) {
            my $i = $rows;
            while ($i >= 0) {
                splice @{ $data->[$i] }, $j, 1;
                ($i,$j) = ($i-1, $seam->[$i][$j]);            
            }
            return 1;
        }
    }
    return 0;
}

sub print_map {
    my $data = shift;
    for (@$data) {
        print join("", @$_), $/;
    }
}

__DATA__
XX...
X....
.....
....X
...XX