Python/project_euler/problem_01/sol2.py

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2018-10-19 12:48:28 +00:00
'''
Problem Statement:
If we list all the natural numbers below 10 that are multiples of 3 or 5,
we get 3,5,6 and 9. The sum of these multiples is 23.
Find the sum of all the multiples of 3 or 5 below N.
'''
from __future__ import print_function
try:
raw_input # Python 2
except NameError:
raw_input = input # Python 3
n = int(raw_input().strip())
sum = 0
terms = (n-1)//3
sum+= ((terms)*(6+(terms-1)*3))//2 #sum of an A.P.
terms = (n-1)//5
sum+= ((terms)*(10+(terms-1)*5))//2
terms = (n-1)//15
sum-= ((terms)*(30+(terms-1)*15))//2
print(sum)