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?
Input data
One number n~(1 \le n \le 90).
Output data
Print one number — the answer to the problem.
Examples
Input example #1
1
Output example #1
1
Input example #2
2
Output example #2
2
Input example #3
3
Output example #3
4