Problems
Out of the line!
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?
\InputFile
One number $n~(1 \le n \le 90)$.
\OutputFile
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