Function-10#2999

Function-10

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128 megabytes

Very easy

Let the function be defined as follows:

f (m, n) = ⎩ ⎨ ⎧ 1, 1, f (m - 1, n - 1) + f (m, n - 1), m = 0 m = n 0 < m < 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}

Compute the value of this function.

Input

Two integers $n$ and $m (0 \leq n, m \leq 20)$ m~(0 \le n, m \le 20).

Print the value of the function $f (m, n)$ f(m, n).

Example 1

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f (m, n) = ⎩ ⎨ ⎧ 1, 1, f (m - 1, n - 1) + f (m, n - 1), m = 0 m = n 0 < m < n

m (0 \leq n, m \leq 20)

f (m, n)