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

##</code><code>##

sub f {
#234567890#234567890#234567890#234567890#234567890#23
$b=1;$b+=1+!($_%4)-!($_%100)+!($_%400)for 1..pop;$b%7
}