Project Euler & HackerRank problem 1 solution: Multiples of 3 and 5 - solved using Python

Project-Euler-Problem-1.py

def sumn(n, d):  # Sum natural numbers ≤ n that are divisible by d
    n //= d
    return d*n*(n+1) // 2
L = int(input('Enter an upper bound? '))
a, b = 3, 5
s = sumn(L-1, a) + sumn(L-1, b) - sumn(L-1, a*b)
print ("Sum of multiples of", a, "or", b, "below", L, "=", s)