Competitions

# 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 (1n90).

#### Output

Print one number – the answer to the problem.

Time limit 1 second
Memory limit 128 MiB
Input example #1
1

Output example #1
1

Input example #2
2

Output example #2
2

Input example #3
3

Output example #3
4