Title: The coding Challenges

Problem: There are n participants appearing for one on one coding challenge.Each participant plays twice (challenges) with each of his opponents.You need to compute the total number of challenges. 

Input: First line contains an integer n, represent number of participants.

Output: Print the total number of challenges.

Constraints: 1≤n≤100

Sample Input: 16

Sample Output: 

240

from operator import mul
from functools import reduce
n= int(input())
if n > 2:
  print(reduce(mul, range(1, n+1)) // reduce(mul, range(1, n-1)))
else:
  print(n // 2)