The Fibonacci numbers, commonly denoted F(n) form a sequence, called the Fibonacci sequence, such that each number is the sum of the two preceding ones, starting from 0 and 1. That is,
F(0) = 0, F(1) = 1 +F(n) = F(n - 1) + F(n - 2), for n > 1. ++ +
Given n, calculate F(n).
+
Example 1:
+ +Input: n = 2 +Output: 1 +Explanation: F(2) = F(1) + F(0) = 1 + 0 = 1. ++ +
Example 2:
+ +Input: n = 3 +Output: 2 +Explanation: F(3) = F(2) + F(1) = 1 + 1 = 2. ++ +
Example 3:
+ +Input: n = 4 +Output: 3 +Explanation: F(4) = F(3) + F(2) = 2 + 1 = 3. ++ +
+
Constraints:
+ +0 <= n <= 30