my $range = Set::IntSpan::Fast->new('50000-65535');
my $ports = Set::IntSpan::Fast->new('50000-51545,51549,51555-51999');

my $unused = $ports->copy;
$unused->invert;

my $unused_in_range = $range->intersection($unused);

my $first_unused = ($unused_in_range->iterate_runs->())[0];
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