B. Number of Words
time limit per test
1 second
memory limit per test
256 megabytes
input
standard input
output
standard output

Write a program to find the number of N-letter «words» composed of the letters A, B, C (by «word» we mean any sequence of consecutive letters) such that there are no more than three letters B in them.

Input

The integer $$$N$$$ ($$$1 \le N \le 20$$$).

Output

Output a single integer — the number of «words» that satisfy the condition.

Example
Input
4
Output
80