"""
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)

"""
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)

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. # Python 2 # Python 3 # sum of an A.P.