Problems
Function-10
Function-10
The function is given with nonnegative integer arguments m and n~(m \le n):
f(m, n) = \begin{cases}
1, m = 0\\
1, m = n\\
f(m - 1, n - 1) + f(m, n - 1), 0 < m < n
\end{cases}
Find the value of the function.
Input data
Two nonnegative integers n and m~(0 \le n, m \le 20).
Output data
Print the value of the function f(m, n).
Examples
Input example #1
4 2
Output example #1
6