Collinearity (ABC181C)

From AtCoder. 3-point collinearity. Solve the geometry problem "Collinearity (ABC181C)".

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

Collinearity (ABC181C)

**From AtCoder.** 3-point collinearity. Solve the geometry problem "Collinearity (ABC181C)".