#include <iostream>
#include <vector>
#include <queue>
using namespace std;


void rec(int N, int first_tower, int second_tower, int third_tower) {
    if(N == 0) {
        return;
    }
    rec(N - 1, first_tower, third_tower, second_tower);
    cout << first_tower << " " << third_tower << endl;
    rec(N - 1, second_tower, first_tower, third_tower);
}
int main() {
    int N;
    cin >> N;
    cout << (1 << N) - 1 << endl;
    rec(N, 1, 2, 3);
    return 0;
}