001 - Fibonacci number

問題

Fibonacci sequence of numbers

F₀ = 0

F₁ = 1

F_n = F_n-1 + F_n-2

In a defined sequence.

Make a program that outputs the n-th Fibonacci sequence.

Input

N

Given the number N of the Fibonacci sequence to be determined in the first line.

Output

You should output the N-th of the Fibonacci sequence.

Constraint

Satisfies the following for all of the input and output case.

• 1 <= N <= 90

Input and output example

Input example Ⅰ

6

Output example Ⅰ

8

Input example Ⅱ

1

Output example Ⅱ

1

Input example Ⅲ

25

Output example Ⅲ

75025