euler19.pl

use 5.010;

# チート
use Date::Simple ('ymd');
use Date::Range;

my $range = Date::Range->new(ymd(1901, 1, 1), ymd(2000, 12, 31));
my @dates = grep { $_->day == 1 and $_->day_of_week == 0 } $range->dates;
say $#dates + 1;