Late night on booze. You gotta be oaking.
Consider this. On the first day of every month you fill your car up with 60 litres of petrol and pay for it. You anticipate this will last you the month. Sadly a day or so before the end of the month you realise you will run out before the first of the next month. You go to the gas station and the minimum you can purchase is 10 litres. You buy the extra. However, on the first day of the following month you go to fill up again but