Sequence

Vasya has become intrigued by creating new sequences and examining them. He wrote the following sequence on the board: 1 2 3 2 3 4 3 4 5 4 5 6 5 6 7 ... Now, Vasya wants to know the position in the sequence where the number k first appears.

Write a program to answer his question.

Input

You are given a natural number k (1 ≤ k ≤ 100).

Output

Output a single number, which is the position where the number k first appears in the sequence. The sequence is indexed starting from one.

Examples