Chemistry

문제

Young Colin has recently started his organic chemistry lessons. His course has begun with the simplest organic molecules called alkanes.

Alkanes are molecules that consist only of hydrogen (H) and carbon (C) atoms. Each carbon atom has exactly 4 bonds (either C−H or C−C bonds), and each hydrogen atom is joined to a carbon atom (H−C bond). An alkane molecule has only single bonds and has no cycles. A molecule with n atoms of carbon always has 2n + 2 atoms of hydrogen and is usually written as C_nH_2n+2.

A series of linked carbon atoms is known as the carbon skeleton. Different carbon skeletons correspond to different alkane structural isomers. Two isomers are considered the same if their carbon skeletons are isomorphic. Alkanes with more than three carbon atoms can be arranged in various different ways. The simplest isomer of an alkane is the one in which the n carbon atoms are arranged in a single chain with no branches. All five isomers of C₆H₁₄ are shown below.

[이미지 1]

As a part of his homework Colin was asked to count the number of different alkane isomers with exactly n carbon atoms. Colin is not able to count them by himself, so he asked you for help.

입력

The only line of the input file contains a single integer number n — the number of carbon atoms in alkane molecule (1 ≤ n ≤ 50).

출력

The only line of output file should contain the number of different C_nH_2n+2 isomers. It is guaranteed that the answer fits signed 64-bit integer type.