title: Inverse of the MonthName() - Function?
body: <p>I've got a month number. By typing in the immediate editor <strong>MonthName(11,True)</strong> I get the result <strong>NOV</strong>. What would be the inverse of this function? e.g. I've got SEP and I want by typing 
  function(SEP) the number 9 as an Output</p>