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Problems

Function-10

Function-10

Time limit 1 second
Memory limit 128 MiB

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