Orz Panda is addicted to one RPG game. To make his character stronger, he have to fulfil tasks to get EXP for higher level.At first he accepted all the tasks.But after he read rules carefully, he realized that what he has done was stupid.
Rule:
Every task costs 1 time interval.
Every task has a dead line.If you can‘t finish it on time ,you have to pay the same amount of gold as the EXP given by this task.
Orz Panda wants to know the minimum amount of gold he has to pay.