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).

Examples

Example 1

Input:  n = 2
Output: 1

F(2) = F(1) + F(0) = 1 + 0 = 1

Example 2

Input:  n = 3
Output: 2

F(3) = F(2) + F(1) = 1 + 1 = 2

Example 3

Input:  n = 4
Output: 3

F(4) = F(3) + F(2) = 2 + 1 = 3

Constraints

• 0 <= n <= 30