# -*- coding: utf-8 -*-
"""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?
"""
def main():
n = 1000
index = 2
p1 = 1
p2 = 2
while len(str(p1)) < n:
p1, p2 = p2, p1 + p2
index += 1
print index
if __name__ == '__main__':
main()