freecodecamp--freecodecamp/curriculum/challenges/english/blocks/daily-coding-challenges-python/69306364df283fcaff2e1ad6.md

id, title, challengeType, dashedName

id	title	challengeType	dashedName
69306364df283fcaff2e1ad6	Challenge 145: Nth Fibonacci Number	29	challenge-145

--description--

Given an integer n, return the nth number in the fibonacci sequence.

The Fibonacci sequence is a series of numbers where each number is the sum of the two preceding ones. The first 10 numbers in the sequence are 0, 1, 1, 2, 3, 5, 8, 13, 21, 34.

--hints--

nth_fibonacci(4) should return 2.

({test: () => { runPython(`
from unittest import TestCase
TestCase().assertEqual(nth_fibonacci(4), 2)`)
}})

nth_fibonacci(10) should return 34.

({test: () => { runPython(`
from unittest import TestCase
TestCase().assertEqual(nth_fibonacci(10), 34)`)
}})

nth_fibonacci(15) should return 377.

({test: () => { runPython(`
from unittest import TestCase
TestCase().assertEqual(nth_fibonacci(15), 377)`)
}})

nth_fibonacci(40) should return 63245986.

({test: () => { runPython(`
from unittest import TestCase
TestCase().assertEqual(nth_fibonacci(40), 63245986)`)
}})

nth_fibonacci(75) should return 1304969544928657.

({test: () => { runPython(`
from unittest import TestCase
TestCase().assertEqual(nth_fibonacci(75), 1304969544928657)`)
}})

--seed--

--seed-contents--

def nth_fibonacci(n):

    return n

--solutions--

def nth_fibonacci(n):
    if n == 1:
        return 0
    if n == 2:
        return 1

    a, b = 0, 1
    for _ in range(3, n + 1):
        a, b = b, a + b
    return b