Pascal's triangle has the property that every number in the triangle is the sum of the two numbers above it.

1
1 1
1 2 1
1 3 3 1
1 4 6 4 1
1 5 10 10 5 1

You are given two integers *R* and *C*. Your task is to find the *C*^{th} number on the *R*^{th} row.

## Input

On the first line read in two space-separated integers *R* and *C* (1 ≤ *C* ≤ *R* ≤ 25).
## Output

On the first and only line output the *C*^{th} number on the *R*^{th} row of Pascal's triangle.
## Sample Input 1

5 2

## Sample Output 1

4