Count Binary Strings

easy
1. You are given a number n.
2. You are required to print the number of binary strings of length n with no consecutive 0's.

Input Format

A number n

Output Format

A number representing the number of binary strings of length n with no consecutive 0's.

Constraints

0 < n <= 45

Notice

Try First, Check Solution later

1. You should first read the question and watch the question video.
2. Think of a solution approach, then try and submit the question on editor tab.
3. We strongly advise you to watch the solution video for prescribed approach.

Example

Input
6
Output
21
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