#970. Stairs: 1-3 steps
A staircase has n steps. Each time you can climb 1 to 3 steps. How many ways are there to reach the top?
### Input
One integer n (1 ≤ n ≤ 50).
### Output
A number.
Examples
Input
16
Output
10609
Input
33
Output
334745777
💡 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.