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#include <bits/stdc++.h>

#define DEBUG(x) cout << '>' << #x << ':' << x << endl;
#define fi first
#define se second
#define ll long long
#define ld long double
#define pb push_back
#define vi vector<int>
#define MAXN 100001

using namespace std;

int calc_rest(int k, vi &values, vi &path) {
    int i = values.size() - 1;
    int cost = 0;
    while (k > 0) {
        if (values[i] > k) {
            i--;
        } else {
            k -= values[i];
            cost++;
            path[i]++;
        }
    }
    return cost;
}

int prepare_values(int k, vi &values) {
    ll next_val = 2;
    values.pb(1);
    int cost = 0;

    while (next_val <= k) {
        values.pb(next_val);
        next_val *= 3;
        cost += 3;
    }

    return cost;
}

int main_path(int N, vi &values, vi &idx, vector<vi> &V) {
    int current = N;
    int next_node = 4;
    idx[0] = N;
    for (int i = 1; i < values.size(); i++) {
        idx[i] = next_node;
        int leftn = next_node - 2;
        int rightn = next_node - 1;

        V[leftn].pb(current);
        V[rightn].pb(current);
        if (leftn > 2) {
            V[leftn].pb(leftn - 3);
            V[rightn].pb(rightn - 3);
        }

        V[next_node].pb(leftn);
        V[next_node].pb(rightn);

        current = next_node;
        next_node += 3;
    }
    return current;
}

int main() {
    ios_base::sync_with_stdio(0);
    cin.tie(0);
    cout.tie(0);

    int k;
    cin >> k;

	if(k == 1) {
		cout<<2<<endl;
		cout<<2<<" "<<-1<<endl;
		cout<<-1<<" "<<-1<<endl;
		return 0;
	}

    vi values;
    int cost = 2;
    cost += prepare_values(k, values);
    // cout << cost << endl;

    vi path(values.size(), 0);
    cost += calc_rest(k, values, path);

    vi idx(values.size());

    int N = cost;
    vector<vi> V(N + 1);

    int next_node = main_path(N, values, idx, V) + 1;
    int parent = 1;

    for (int i = values.size() - 1; i >= 0; i--) {
        for (int j = 0; j < path[i]; j++) {
            V[parent].pb(next_node);
            V[next_node].pb(idx[i]);
            parent = next_node;
            next_node++;
        }
    }

    for (int i = 0; i < V.size(); i++)
        while (V[i].size() < 2) {
            V[i].pb(-1);
        }

    cout << N << endl;
    for (int i = 1; i < V.size(); i++)
    	cout<<V[i][0]<<" "<<V[i][1]<<endl;
        // cout << i << ": " << V[i][0] << " " << V[i][1] << endl;

    return 0;
}