[UCSD白板题 ]Small Fibonacci Number

Problem Introduction

The Fibonacci numbers are defined as follows: \(F_0=0\), \(F_1=1\),and \(F_i=F_{i-1}+F_{i-2}\) for $ i \geq 2$.

Problem Description

Task.Given an integer \(n\)，find the \(n\)th Fibonacci number \(F_n\).

Input Format.The input consists of a single integer \(n\).

Constraints.\(0 \leq n \leq 45\).

Output Format.Output \(F_n\).

Sample 1.
Input:

3

Output

2

Sample 2.
Input:

10

Output:

55

Solution

# Uses python3
def calc_fib(n):
    x,y = 0,1
    while n > 0:
        x,y,n = y,x+y,n-1
    return x
n = int(input())
print(calc_fib(n))