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#include <bits/stdc++.h>

using namespace std;

struct TestCase
{
  int path_count;
};

TestCase read_test_case();
void solve_test_case(const TestCase&);

int main()
{
  ios_base::sync_with_stdio(false);
  cin.tie(NULL);
  solve_test_case(read_test_case());
}

TestCase read_test_case()
{
  TestCase test_case;
  cin >> test_case.path_count;
  return test_case;
}

struct Node
{
  int first, second;
};

void solve_test_case(const TestCase& test_case)
{
  vector<Node> nodes;

  for (int i = 1; (1 << ((i - 1) / 2)) <= test_case.path_count; i++)
  {
    if (i % 2 == 1)
      nodes.push_back({i + 1, i + 2});
    else
      nodes.push_back({i + 1, -1});
  }

  // Last two nodes here are kinda special
  nodes[nodes.size() - 1].first = -1;
  nodes[nodes.size() - 2].second = -1;

  nodes.push_back({-1, -1});
  int last_node = nodes.size();
  int k = test_case.path_count;
  for (int i = 0; (1 << i) <= test_case.path_count; i++)
  {
    if ((1 << i) & k)
    {
      int index = 2 * i + 1;
      nodes[index].second = last_node;
    }
  }

  cout << last_node << "\n";
  for (auto n : nodes) { cout << n.first << " " << n.second << "\n"; }
}