Y. Number of Ways
time limit per test
1 second
memory limit per test
256 megabytes
input
standard input
output
standard output

Given two numbers $$$S$$$ and $$$E$$$ where $$$S$$$ denotes a start point and $$$E$$$ denotes an end point. Determine how many possible ways to reach point $$$E$$$ if you can move either 1 step, 2 steps or 3 steps at a time.

Note: Solve this problem using recursion.

Input

Only one line contains two numbers $$$S$$$ and $$$E$$$ $$$ (1 \le S \le E \le 15 )$$$.

Output

Print the answer required above.

Example
Input
2 5
Output
4
Note

In the first example:

There are 4 ways to reach from point 2 to point 5 as follows: [2, 3, 4, 5], [2, 3, 5], [2, 4, 5] and [2, 5].