my @days = qw(Sunday Monday Tuesday Wednesday Thursday Friday Saturday);

my $day = f($ARGV[0] || 2001);
print $days[$day], $/;

sub f {
#234567890#234567890#234567890#234567890#234567890#234567890#234567890#234567890
$b=1;for(1..pop){$b++;$b++if!$_%4;$b--if!$_%100;$b++if!$_%400}$b%=7
}