Combination

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Codeforces

Easy

Combinatorics

Math

Combination

Compute the number of ways to choose $m$ items from $n$ distinct items.

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Codeforces 155B

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Problem Statement

Given two integers $n$ and $m$ , determine how many different groups of size $m$ can be formed from $n$ distinct items.

This is the standard combination count, often written as $C(n,m)$ or ${n \choose m}$ .

You may assume the inputs are valid and fit in normal integer ranges for the intended solution approach.

Input Format

Two integers $n$ and $m$ .
They represent the total number of distinct items and the size of the group to choose.

Output Format

Print a single integer: the number of ways to choose exactly $m$ items from $n$ distinct items.

Constraints

$0 \le m \le n$
$n$ is small enough that the result fits in the expected integer type for the problem setting.

Examples

Sample cases returned by the problem API.

Example 1

Input

5 2

Output

Explanation

There are $\binom{5}{2} = 10$ ways to choose 2 items from 5 distinct items.

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