#971. Stairs: steps 2, 3
A staircase has n steps. Each time you can climb 2, 3 steps. How many ways are there to land exactly on the top?
### Input
One integer n (1 ≤ n ≤ 60).
### Output
A number.
Examples
Input
21
Output
151
Input
53
Output
1221537
💡 You can solve it with Python, JavaScript or blocks. Read the input line by line with input(). Don't print a question (like input("Number: ")). Print exactly what the output asks for, nothing more.