Convex Hull (Graham Scan)

From CSES. Graham Scan / Monotone Chain. Solve the geometry problem "Convex Hull (Graham Scan)".

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

Convex Hull (Graham Scan)

**From CSES.** Graham Scan / Monotone Chain. Solve the geometry problem "Convex Hull (Graham Scan)".