You are the king of Pensville where you have $2N$ workers.
All workers will be grouped in association of size 2,so a total of N associations have to be formed.
The building speed of the $i^{th}$ worker is $A_i$.
To make an association, you pick up 2 workers. Let the minimum building speed between both workers be x, then the association has the resultant building speed x.
You have to print the maximum value possible of the sum of building speeds of N associations if you make the associations optimally.

Constraints
$1 \le N \le 5 * 10^4$
$1 \le A_i \le 10^4$

Input
First line contains an integer N, representing the number of associations to be made.
Next line contains $2N$ space separated integers, denoting the building speeds of $2N$ workers.

Output
Print the maximum value possible of the sum of building speeds of all the associations.