Problem_25.py

# 1000-digit Fibonacci number
# Problem 25
# https://projecteuler.net/problem=25

# The Fibonacci sequence is defined by the recurrence relation:
#
# Fn = Fn−1 + Fn−2, where F1 = 1 and F2 = 1.
# Hence the first 12 terms will be:
#
# F1 = 1
# F2 = 1
# F3 = 2
# F4 = 3
# F5 = 5
# F6 = 8
# F7 = 13
# F8 = 21
# F9 = 34
# F10 = 55
# F11 = 89
# F12 = 144
# The 12th term, F12, is the first term to contain three digits.
#
# What is the index of the first term in the Fibonacci sequence to contain 1000 digits?

# Answer: 4782.

n = 1000
check: str = ''
fib1 = fib2 = 1
answer: int = 0
count: int = 0
while len(check) != n:
    fib1, fib2 = fib2, fib1 + fib2
    check = str(fib2)
    count += 1
answer = count + 2
print('Answer:', answer)