Kata

The accounts of the "Fat to Fit Club (FFC)" association are supervised by John as a volunteered accountant. The association is funded through financial donations from generous benefactors. John has a list of the first n donations: [14, 30, 5, 7, 9, 11, 15] He wants to know how much the next benefactor should give to the association so that the average of the first n + 1 donations should reach an average of 30. After doing the math he found 149. He thinks that he could have made a mistake.

Could you help him?

Task

The function should return the expected donation (rounded up to the next integer) that will permit to reach the average.

Should the last donation be a non positive number (<= 0) John wants us either to throw an error or return such value so he will clearly see that his expectations are not great enough.

In "Sample Tests" you can see what to return.

Notes:

• all donations and new average are numbers (integers or floats), array of donations can be empty.
• See examples below and "Sample Tests" to see which return is to be done.

array: [14, 30, 5, 7, 9, 11, 15], new average: 92 -> result: 645
array: [14, 30, 5, 7, 9, 11, 15], new average: 2  -> result: variable, see "Sample Tests"