#include <bits/stdc++.h>

using namespace std;

// 次数 4 の頂点が一部最適解 (確率が足りない)
int main(int argc, char* argv[]) {
    int N = 199995;
    int L = 39999;  // 列の個数
    vector<vector<int>> G(N + 1);

    for (int i = 1; i < L; i++) {
        G[i].push_back(i + 1);
        G[i + 1].push_back(i);
    }
    int id = L + 1;

    for (int u = 1; u <= L; u++) {
        int now = u;

        G[now].push_back(id);
        G[id].push_back(now);
        now = id;
        id++;
        G[now].push_back(id);
        G[id].push_back(now);
        id++;

        now = u;
        G[now].push_back(id);
        G[id].push_back(now);
        now = id;
        id++;
        G[now].push_back(id);
        G[id].push_back(now);
        id++;
    }

    stack<int> S;
    S.push(1);
    vector<int> visited(N + 1, 0);

    cout << N << endl;
    while (!S.empty()) {
        int now = S.top();
        S.pop();
        visited[now] = 1;

        for (int nx : G[now]) {
            if (visited[nx]) continue;
            cout << min(now, nx) << " " << max(nx, now) << "\n";
            S.push(nx);
        }
    }

    return 0;
}