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#include <bits/stdc++.h>
#define fi first
#define se second
#define pb push_back

using namespace std;
typedef long long ll;
typedef pair<int, int> pii;
typedef pair<long long, long long> pll;

int k;
vector<int> G[109];

void connect(int from, int to) { G[from].pb(to); }

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

    cin >> k;
    int cnt = 0;
    for (int i = 1; i <= k; i *= 2) cnt++;

    for (int i = 1; i < cnt; i++)
    {
        connect(i, i + 1);
    }

    for (int i = 1; i < cnt; i++)
    {
        connect(i, cnt + i);
        connect(cnt + i, i + 1);
    }

    connect(cnt, 2 * cnt);

    int n = 2 * cnt;
    int pt = cnt + 1;
    while (k > 1)
    {
        if (k % 2 == 1) connect(pt, n);
        k /= 2;
        pt++;
    }

    cout << n << "\n";
    for (int i = 1; i <= n; i++)
    {
        if (G[i].size() == 0)
        {
            cout << "-1 -1\n";
        }
        else if (G[i].size() == 1)
        {
            cout << G[i][0] << " " << -1 << "\n";
        }
        else
        {
            cout << G[i][0] << " " << G[i][1] << "\n";
        }
    }
}