Problem:
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

Solution in Python (3.4.3) (judge verdict: Accepted)

import math
def getInt(): return int(input())
def getIntList(): return [int(x) for x in input().split()]
def zeros(n): return [0]*n
def zeros2(n, m): return [zeros(m) for i in range(n)] # obsoleted zeros((n, m))で代替

class Debug():
    def __init__(self):
        self.debug = True
 
    def off(self):
        self.debug = False
 
    def dmp(self, x, cmt=''):
        if self.debug:
            if cmt != '':
                w = cmt + ': ' + str(x)
            else:
                w = str(x)
            print(w)
        return x

def prob():  # WA 2
    d = Debug()
    d.off()
    N = getInt()
    d.dmp((N), 'N')
    L = getIntList()
    d.dmp((L), 'L')
    L.sort()
    count = 0
    for i in range(N):
        count += min(L[i*2], L[i*2+1])
    return count


ans = prob()
print(ans)