Triangles from Matches#35

Triangles from Matches

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Kleptyk, known from the Match Model problem, decided to demonstrate his skills again. He began constructing triangles using matches.

What is the minimal number of matches needed to form $n$ triangles, if each side of a triangle is formed by a single match?

Input

The input contains a single integer $n$ ( $n < 2 \cdot 1 0^{9}$ n < 2 \cdot 10^9).

Print the minimal number of matches required to form $n$ triangles.

Example 1

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n < 2 \cdot 1 0^{9}