You can't solve the same old problem with the same old thinking on monday and tuesday, so give it a rest. That's right. While "roductivity" is a big buzzword, it's just as important to remember that you can't have high productivity without an equal amount of break time to give yourself a chance to come at the situation from a new angle. Take an unorthodox approach, or at least consider taking an unorthodox approach, on wednesday and thursday. Be open to any ideas. By friday, your open-minded attitude (and a good dose of serendipity) will lead you where you need to be.