//  Tower of Hanoi

#include <bits/stdc++.h>
using namespace std;

void hanoi(deque<int> &current, deque<int> &destination, deque<int> &tmp, int n, vector<pair<int, int>> &remember, tuple<int, int, int> stack_names) {
    if (n == 1) {
        auto top = current.back();
        current.pop_back();
        destination.push_back(top);
        remember.push_back({get<0>(stack_names), get<1>(stack_names)});
        return;
    }
    hanoi(current, tmp, destination, n - 1, remember, {get<0>(stack_names), get<2>(stack_names), get<1>(stack_names)});
    auto top = current.back();
    current.pop_back();
    destination.push_back(top);
    remember.push_back({get<0>(stack_names), get<1>(stack_names)});
    hanoi(tmp, destination, current, n - 1, remember, {get<2>(stack_names), get<1>(stack_names), get<0>(stack_names)});
    return ;
};

int main() {
    int size;
    cin >> size;
    deque<int> start;
    deque<int> s2;
    deque<int> s3;
    for (int i = size; i > 0; i--) {
        start.push_front(i);
    }
    vector<pair<int, int>> r;                                                                       //c, t, d
    hanoi(start, s2, s3, size, r, {1, 3, 2});
    cout << r.size() << endl;
    for (auto &[a, b]: r) cout << a << " " << b << endl;
    cout << endl;
    return 0;
}