Vanya and Triangles

From Codeforces. Count non-degenerate triangles from points. Solve the geometry problem "Vanya and Triangles".

Examples
Input: [1,2,3]
Output: 0
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Vanya and Triangles

**From Codeforces.** Count non-degenerate triangles from points. Solve the geometry problem "Vanya and Triangles".