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34 lines
757 B
Python
34 lines
757 B
Python
"""
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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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def solution(n):
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"""Returns the sum of all the multiples of 3 or 5 below n.
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>>> solution(3)
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0
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>>> solution(4)
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3
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>>> solution(10)
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23
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>>> solution(600)
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83700
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"""
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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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return sum
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if __name__ == "__main__":
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print(solution(int(input().strip())))
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