Given n .You can choose n points in a circle and you have to draw lines joining them.Condition is each point can lie in only one line and no two lines can  intersect.You have to count number of line sequences possible.A line sequence is possible when we can draw lines from each points and satisfying the condtion mentioned above.

**Constraints**
1<=n<=50

Inputs
2
Output 
1

Inputs
4
Output 
2

Inputs
6
Output 
5

How to solve this?