/* -*- coding: utf-8 -*-
 *
 * 3704.cc:  No.3704 豌励∪縺壹＞繝壹い (Awkward Pairs) - yukicoder
 */

#include<cstdio>
#include<algorithm>
#include<utility>

using namespace std;

/* constant */

const int MAX_N = 200000;
const int MAX_N2 = MAX_N * 2;

/* typedef */

using ll = long long;
using pii = pair<int,int>;

/* global variables */

int as[MAX_N2];
pii ais[MAX_N2];

/* subroutines */

/* main */

int main() {
  int n;
  scanf("%d", &n);
  int n2 = n * 2;
  for (int i = 0; i < n2; i++) scanf("%d", as + i);

  for (int i = 0; i < n2; i++) ais[i] = {as[i], i};
  sort(ais, ais + n2);

  ll sum = 0;
  for (int i = 0; i < n; i++)
    sum += ais[n2 - 1 - i].first - ais[i].first;

  printf("%lld\n", sum);
  for (int i = 0; i < n; i++)
    printf("%d %d\n", ais[i].second + 1, ais[n2 - 1 - i].second + 1);
  
  return 0;
}