#!/usr/local/bin/perl
use 5.012;
my $head = 0x0000_0000_0000_0000;
my $tail = 0x7fff_ffff_ffff_ffff;
my ($when, $next);
while ($next = $head + $tail >> 1) {
    last if $when == $next;
    $when = $next;
    # warn "$head, $when, $tail";
    !!(gmtime $when) ? $head = $when + 1 : $tail = $when - 1;
}
say $when;
say scalar gmtime $when;
say scalar localtime $when;
say scalar gmtime $when+1;