Return the n-th Fibonacci number, where F(0) = 0, F(1) = 1 and F(k) = F(k-1) + F(k-2).
Input
A single integer n.
Output
F(n).
Nth Fibonacci Number
Easydynamic-programmingmath
Examples
Example 1
- Input
0
- Output
0
F(0) = 0.
Example 2
- Input
1
- Output
1
F(1) = 1.
Example 3
- Input
10
- Output
55
F(10) = 55.
Constraints
- 0 <= n <= 90 (F(90) still fits in 64-bit).
Hints
Reveal hint 1
Build up iteratively from F(0) and F(1) — no recursion needed.
Reveal hint 2
Keep only the last two values as you go.
Reference solution (spoiler — try it yourself first)
Approach
Iterate n times, keeping the previous two Fibonacci numbers (a, b) and stepping (a, b) → (b, a + b).
n = int(input())
a, b = 0, 1
for _ in range(n):
a, b = b, a + b
print(a)
Bring us the problem, not a perfect specification
Tell us what needs to change, who it affects and any important deadline. We will review the context and reply with useful next questions.
- 01Share contextDescribe the workflow, constraint or risk.
- 02Clarify togetherWe identify missing facts and useful options.
- 03Choose a startAgree a focused assessment or delivery step.