eolymp
Competitions

ISSPS`13 Wave 2 Day 5

Out of the line!

Time limit 1 second
Memory limit 128 MiB

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 (1n90).

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