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"""
Problem:
Each new term in the Fibonacci sequence is generated by adding the previous two
terms. By starting with 1 and 2, the first 10 terms will be:
1,2,3,5,8,13,21,34,55,89,..
By considering the terms in the Fibonacci sequence whose values do not exceed
n, find the sum of the even-valued terms. e.g. for n=10, we have {2,8}, sum is
10.
"""
import math
from decimal import Decimal, getcontext
def solution(n):
"""Returns the sum of all fibonacci sequence even elements that are lower
or equals to n.
>>> solution(10)
10
>>> solution(15)
10
>>> solution(2)
2
>>> solution(1)
0
>>> solution(34)
44
>>> solution(3.4)
2
>>> solution(0)
Traceback (most recent call last):
...
ValueError: Parameter n must be greater or equal to one.
>>> solution(-17)
Traceback (most recent call last):
...
ValueError: Parameter n must be greater or equal to one.
>>> solution([])
Traceback (most recent call last):
...
TypeError: Parameter n must be int or passive of cast to int.
>>> solution("asd")
Traceback (most recent call last):
...
TypeError: Parameter n must be int or passive of cast to int.
"""
try:
n = int(n)
except (TypeError, ValueError) as e:
raise TypeError("Parameter n must be int or passive of cast to int.")
if n <= 0:
raise ValueError("Parameter n must be greater or equal to one.")
getcontext().prec = 100
phi = (Decimal(5) ** Decimal(0.5) + 1) / Decimal(2)
index = (math.floor(math.log(n * (phi + 2), phi) - 1) // 3) * 3 + 2
num = Decimal(round(phi ** Decimal(index + 1))) / (phi + 2)
sum = num // 2
return int(sum)
if __name__ == "__main__":
print(solution(int(input().strip())))