Sharygin 2012/8

From Olympiad. Right triangle angle B = 90 midpoint M. Solve the geometry problem "Sharygin 2012/8".

Examples
Input: [1,2,3]
Output: 0
Hints

Sharygin 2012/8

**From Olympiad.** Right triangle angle B = 90 midpoint M. Solve the geometry problem "Sharygin 2012/8".