/* -*- coding: utf-8 -*-
 *
 * 2519.cc:  No.2519 Coins in Array - yukicoder
 */

#include<cstdio>
#include<algorithm>
#include<utility>
 
using namespace std;

/* constant */

const int MAX_N = 200000;

/* typedef */

typedef long long ll;
typedef pair<int,int> pii;

/* global variables */

int as[MAX_N];
pii ops[MAX_N];

/* subroutines */

template <typename T>
T gcd(T m, T n) {  // m >= 0, n >= 0
  if (m < n) swap(m, n);
  while (n > 0) {
    T r = m % n;
    m = n;
    n = r;
  }
  return m;
}

ll f(ll x, ll y) {
  ll g = gcd(x, y);
  return (g == 1) ? (x - 1) * (y - 1) : 0;
}

/* main */

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

  ll mina = 0;
  if (n == 2) {
    mina = f(as[0], as[1]);
    ops[0] = pii(0, 1);
  }
  else if (n == 3) {
    ll f0 = f(f(as[0], as[1]), as[2]);
    ll f1 = f(f(as[0], as[2]), as[1]);
    ll f2 = f(f(as[1], as[2]), as[0]);
    if (f0 <= min(f1, f2))
      mina = f0, ops[0] = pii(0, 1);
    else if (f1 <= f2)
      mina = f1, ops[0] = pii(0, 2);
    else
      mina = f2, ops[0] = pii(1, 2);
    ops[1] = pii(0, 1);
  }
  else {
    mina = 0;
    for (int i = 0; i < n - 1; i++) ops[i] = pii(0, 1);
  }

  printf("%lld\n", mina);
  for (int i = 0; i < n - 1; i++)
    printf("%d %d\n", ops[i].first + 1, ops[i].second + 1);

  return 0;
}