function a($b)
    dim $c,$,$d,$!
    $=join(split($b,_),$)
    while $
        $d=$c<'/'
        $c=$
        $=right($,~)
        $d=$d+($<'/')
        $!=$!+iif($c>_,$d,2*($c<'/'|$c<_&$d))
;    loop
    $a=$!*50/($b^)
endfunction