Fibonacci Number 2

The Fibonacci sequence starts with 0 and 1. The 0th Fibonacci number is 0, and the 1st Fibonacci number is 1. From the 2nd term onward, each Fibonacci number is the sum of the two immediately preceding Fibonacci numbers.

As a formula, for n >= 2, F_n = F_{n-1} + F_{n-2}.

The Fibonacci numbers up to n = 17 are as follows.

0, 1, 1, 2, 3, 5, 8, 13, 21, 34, 55, 89, 144, 233, 377, 610, 987, 1597

Given n, write a program that computes the nth Fibonacci number.

The first line contains a natural number n. The value of n is at most 90.

Print the nth Fibonacci number on the first line.