P1036 [NOIP 2002 Junior] Choosing Numbers

Description

Given $n$ integers $x_1, x_2, \cdots, x_n$, and one integer $k$ ($k

Input Format

The first line contains two integers $n, k$ separated by a space ($1 \le n \le 20$, $k

Output Format

Output a single integer representing the number of ways.

Explanation/Hint

【Source】 NOIP 2002 Junior, Problem 2. Translated by ChatGPT 5