Ruter chaos

Here in Oslo, all busses, trams etc are operated by # Ruter. They have converted all tickets to something called Flexus. As a part of that, I now have to charge a card with money, instead of buying N tickets. And for some bizarre reason, I cannot simply charge it with 50 tickets, I have to charge it with even sums of money (in 50NOK increments from my experience). Thus I made a small calculator to calculate how much I would have to recharge, given my current balance, to achieve an even number of tickets.