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