#include <string.h>
#include <algorithm>
#include <array>
#include <bitset>
#include <cassert>
#include <cfloat>
#include <climits>
#include <cmath>
#include <complex>
#include <ctime>
#include <deque>
#include <fstream>
#include <functional>
#include <iomanip>
#include <iostream>
#include <iterator>
#include <list>
#include <map>
#include <memory>
#include <queue>
#include <random>
#include <set>
#include <stack>
#include <string>
#include <unordered_map>
#include <unordered_set>
#include <utility>
#include <vector>
using namespace std;

int main() {
    ios::sync_with_stdio(false);
    cin.tie(nullptr);
    cout << 180003 << "\n";
    cout << 1 << " " << 2 << "\n";
    cout << 1 << " " << 3 << "\n";
    cout << 2 << " " << 4 << "\n";
    cout << 2 << " " << 5 << "\n";
    cout << 2 << " " << 6 << "\n";
    cout << 3 << " " << 7 << "\n";
    cout << 3 << " " << 8 << "\n";
    cout << 3 << " " << 9 << "\n";
    for(int i = 10; i <= 180003; i++) {
        cout << i-6 << " " << i << "\n";
    }
}