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Score : $200$ points

### Problem Statement

Snuke is having a barbeque party.

At the party, he will make $N$ servings of Skewer Meal.

Example of a serving of Skewer Meal

He has a stock of $2N$ skewers, all of which will be used in Skewer Meal. The length of the $i$-th skewer is $L_i$. Also, he has an infinite supply of ingredients.

To make a serving of Skewer Meal, he picks $2$ skewers and threads ingredients onto those skewers. Let the length of the shorter skewer be $x$, then the serving can hold the maximum of $x$ ingredients.

What is the maximum total number of ingredients that his $N$ servings of Skewer Meal can hold, if he uses the skewers optimally?

### Constraints

• $1≦N≦100$
• $1≦L_i≦100$
• For each $i$, $L_i$ is an integer.

### Input

The input is given from Standard Input in the following format:

$N$
$L_1$ $L_2$ $...$ $L_{2N}$


### Output

Print the maximum total number of ingredients that Snuke's $N$ servings of Skewer Meal can hold.

### Sample Input 1

2
1 3 1 2


### Sample Output 1

3


If he makes a serving using the first and third skewers, and another using the second and fourth skewers, each serving will hold $1$ and $2$ ingredients, for the total of $3$.

### Sample Input 2

5
100 1 2 3 14 15 58 58 58 29


### Sample Output 2

135