#include <bits/stdc++.h>
using namespace std;

#define rep(i, a, b) for (ll i = a; i < b; i++)
using ll = long long;

int main(){
    int n;
    cin >> n;
    int n2 = n * 2;
    using P = pair<int, int>;
    vector<P> a(n2);
    rep(i, 0, n2) {
        cin >> a[i].first;
        a[i].second = i;
    }
    sort(a.begin(), a.end());
    ll ans = 0;
    int l = 0, r = n2 - 1;
    while(l < r) {
        ans += a[r].first - a[l].first;
        l++;
        r--;
    }
    cout << ans << endl;
    l = 0, r = n2 - 1;
    while(l < r) {
        cout << a[l].second + 1 << " " << a[r].second + 1 << endl;
        l++;
        r--;
    }
}