Python/project_euler/problem_01/sol3.py

from __future__ import print_function

'''
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.
'''
'''
This solution is based on the pattern that the successive numbers in the series follow: 0+3,+2,+1,+3,+1,+2,+3.
'''

try:
    raw_input          # Python 2
except NameError:
    raw_input = input  # Python 3
n = int(raw_input().strip())
sum=0
num=0
while(1):
    num+=3
    if(num>=n):
        break
    sum+=num
    num+=2
    if(num>=n):
        break
    sum+=num
    num+=1
    if(num>=n):
        break
    sum+=num
    num+=3
    if(num>=n):
        break
    sum+=num
    num+=1
    if(num>=n):
        break
    sum+=num
    num+=2
    if(num>=n):
        break
    sum+=num
    num+=3
    if(num>=n):
        break
    sum+=num

print(sum);