snake_case all the things

project_euler/problem_01/sol2.py

@@ -0,0 +1,20 @@
+'''
+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)