Mock CCO '19 Contest 1 Problem 4 - A Chemistry Problem

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Points: 15 (partial)
Time limit: 0.6s
Memory limit: 162M

Problem types

A circle is drawn with center at O and N points p_1 through p_N are equally spaced around the circle.

Line segments are drawn to connect O to each of these N points.

Compute the number of ways to delete N of the line segments or arcs such that the N+1 points are still connected.


1 \le N \le 100

In test data worth 10% of marks, you may assume N \le 10.

Input Specification

The first and only line contains a single positive integer, N.

Output Specification

Output the number of desired configurations.

Sample Input


Sample Output



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