--- /dev/null
+#!/usr/bin/perl -w
+
+use strict;
+use v5.30;
+
+chomp (my $line = <>);
+
+my $traps;
+for (1 .. 400000) {
+ $traps += () = $line =~ /\./g;
+ say $traps if $_ == 400000;
+ $line = '.' . $line . '.';
+ my $nl = '';
+ for my $i (0 .. length($line)-3) {
+ my $p = substr($line, $i, 3);
+ $nl .= ($p eq '^^.' || $p eq '.^^' || $p eq '^..' || $p eq '..^')
+ ? '^' : '.';
+ }
+ # say "$_ $nl";
+ $line = $nl;
+}
+