Competitions

# October 7 - BMTK Programming School, High League

# Out of the line!

**n** soldiers stay in one line. In how many ways can we choose some of them (at least one) so that among them there will not be soldiers standing beside?

#### Input

One number **n** (**1** ≤ **n** ≤ **90**).

#### Output

Print one number – the answer to the problem.

Input example #1

1

Output example #1

1

Input example #2

2

Output example #2

2

Input example #3

3

Output example #3

4