eolymp
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 (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