P6352 [COCI 2007/2008 #3] CETIRI

You originally had $4$ numbers. After sorting them in ascending order, they form an arithmetic progression. Now one number is missing, and the order of the remaining three numbers has also been shuffled. Please find the fourth number.

Input one line with three integers. It is guaranteed that these numbers are in the range $-100\sim 100$.

Output one line with one number, the fourth number. **The solution may not be unique, but it is guaranteed that at least one solution exists. This problem uses SPJ.**

#### Explanation **Translated from [COCI2007-2008](https://hsin.hr/coci/archive/2007_2008/) [CONTEST #3](https://hsin.hr/coci/archive/2007_2008/contest3_tasks.pdf) *T1 CETIRI***。 Translated by ChatGPT 5