Problem:
Score : 300 points

Problem Statement

There are 3N participants in AtCoder Group Contest.
The strength of the i-th participant is represented by an integer a_i.
They will form N teams, each consisting of three participants.
No participant may belong to multiple teams.

The strength of a team is defined as the second largest strength among its members.
For example, a team of participants of strength 1, 5, 2 has a strength 2, and a team of three participants of strength 3, 2, 3 has a strength 3.

Find the maximum possible sum of the strengths of N teams.

Constraints

1 ≤ N ≤ 10^5

1 ≤ a_i ≤ 10^{9}

a_i are integers.

Input

Input is given from Standard Input in the following format:

N
a_1 a_2 ... a_{3N}

Output

Print the answer.

Sample Input 1

2
5 2 8 5 1 5

Sample Output 1

10

The following is one formation of teams that maximizes the sum of the strengths of teams:

Team 1: consists of the first, fourth and fifth participants.

Team 2: consists of the second, third and sixth participants.

Sample Input 2

10
1000000000 1000000000 1000000000 1000000000 1000000000 1000000000 1000000000 1000000000 1000000000 1000000000 1000000000 1000000000 1000000000 1000000000 1000000000 1000000000 1000000000 1000000000 1000000000 1000000000 1000000000 1000000000 1000000000 1000000000 1000000000 1000000000 1000000000 1000000000 1000000000 1000000000

Sample Output 2

10000000000

The sum of the strengths can be quite large.

Solution in C (Clang 3.8.0) (judge verdict: Runtime Error)

// https://atcoder.jp/contests/agc012/tasks/agc012_a
// A - AtCoder Group Contest
#include <stdio.h>
#include <stdlib.h>
#include <string.h>

// 標準入力から改行かスペースまで読み取り、数字として返す
int get_num() {
    // 10文字+区切り文字までしか受け付けられない
    char s[11];
    int i, n;
    // scanf()の直後は改行が入力に残っているので、
    // 最初の改行は読み飛ばす
    do {
        s[0] = getchar();
    } while (s[0] == '\0' || s[0] == '\n');
    for (i = 1; i < sizeof(s); i++) {
        s[i] = getchar();
        if (s[i] == ' ' || s[i] == '\n') {
            s[i] = '\0';
            break;
        }
    }
    sscanf(s, "%d", &n);
    return n;
}


// intバブルソート
void sort(int a[], int num) {
    int i, j, b;
    for (i = 0; i < num-1; i++) {
        for (j = 0; j < num-i-1; j++) {
            if (a[j] > a[j+1]) {
                b = a[j];
                a[j] = a[j+1];
                a[j+1] = b;
            }
        }
    }
}

int main(void) {
    int a[30000];
    int n;
    long sum = 0;
    n = get_num();
    
    for (int i = 0; i < 3 * n; i++) {
        a[i] = get_num();
    }

    sort(a, n*3);
    
    for (int i = 0; i < n; i++) {
        sum += a[n*3-1 - (i*2+1)];
    }
    
    // 1 2 3 4    6 7
    // 1 2 3 4 5 6
    // 5 2 8 5 1 5
    // 1 2  5 5 5 8
    
    printf("%ld", sum);
    
    return 0;
}