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

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


int main(){
    int n;  cin >> n;
    vector<ll> a(n);
    for(auto& x : a){
        cin >> x;
    }
    
    ll ans = 0;
    vector<pair<int, int> > ops = {};
    if(n == 2){
        ans = f(a[0], a[1]);
        ops = { {1, 2} };
    }
    else if(n == 3){
        ans = f(f(a[0], a[1]), a[2]);
        ops = { {1, 2}, {1, 2} };
        ll t = f(f(a[0], a[2]), a[1]);
        if(t < ans){
            ans = t;
            ops = { {1, 3}, {1, 2} };
        } 
        t = f(f(a[1], a[2]), a[0]);
        if(t < ans){
            ans = t;
            ops = { {2, 3}, {1, 2} };
        }       
    }
    else{
        ans = 0;
        ops = { {1, 2}, {1, 2}, {n - 3, n - 2} };
        for(int i = n - 3; i > 1; --i){
            ops.push_back({1, i});
        }
    }

    cout << ans << endl;
    for(auto&[x, y] : ops){
        cout << x << ' ' << y << endl;
    }
    
    return 0;
}