Find nCr (Combination formula) recursively using Pascal's relation.

Difficulty: Hard

Phase: 3 · Recursion

XP Reward: 30 XP

Topics: Recursion, Hard

Supported Languages: Python, JavaScript, C, C++, Java

Problem Description

Given N and R (0 <= R <= N) on separate lines, compute combination nCr using Pascal's recursive relation nCr = (n-1)C(r-1) + (n-1)Cr. Input Format: Read input from standard input (stdin). Output Format: Print the result to standard output (stdout).

Constraints

-10^9 <= N <= 10^9

Examples

Example 1

Input: 5 2

Output: 10

Explanation: Sample execution for input 5 2