calculate-the-permutation-of-n-objects-taken-r-at-a-time.py

def factorial(x ) :
    
    if x == 1 or  0  :
        return 1
    return x*factorial(x-1)
n , r = map(int , input().split())

# number permuation = y

a = factorial(n)
b = factorial(n-r)
print(a//b)