#include <bits/stdc++.h>

using namespace std;

int n;
vector<pair<int, int> > rj;

void play (int x, int y) {
    rj.push_back ({x, y});
}

void tri () {
    play (2, 3);
    play (3, 1);
    play (2, 2);
    play (1, 1);
    play (3, 3);
    play (3, 2);
    play (1, 2);
    play (1, 3);
    play (2, 1);
}

void cetiri () {
    play (1, 1);
    play (2, 4);
    play (1, 4);
    play (2, 1);
    play (3, 1);
    play (4, 1);
    play (4, 4);
    play (3, 4);
    play (1, 2);
    play (2, 2);
    play (4, 3);
    play (2, 3);
    play (3, 3);
    play (3, 2);
}

void par (int x) {
    play (x - 2, x);
    play (x - 2, x - 1);
    play (x - 1, x);
    play (x - 1, x - 2);
    play (x, x - 2);
    play (x - 1, x - 1);
    play (x, x - 1);
    play (x, x);
}

void nepar (int x) {
    play (x - 1, x);
    play (x - 2, x - 1);
    play (x, x - 1);
    play (x - 1, x - 1);
    play (x - 2, x);
    play (x, x - 2);
    play (x - 1, x - 2);
    play (x, x);
}

void solve (int x) {
    if (x == 3) {
        tri ();
        return;
    }
    if (x == 4) {
        cetiri ();
        return;
    }

    solve (x - 2);

    for (int i = 0; i < x - 3; i++) {
        int prvi = (x - 2) + 0 + i + 0 + i + max ((x - (i + 1) - 1), 0) + 1 + 0;
        if (i == 0) prvi -= 2;

        int drugi = (x - 2) + 0 + i + 0 + max (i - 1, 0) + max ((x - (i + 1) - 3), 0) + 0 + 0;

        if (prvi % 2 == 0) {
            play (x - 1, i + 1);
            play (x, i + 1);
        }
        else {
            play (x, i + 1);
            play (x - 1, i + 1);
        }

        prvi = i + 0 + (x - 2) + 0 + i + i + (x - 2 - (i - 1)) + 0;
        if (i == 0) prvi--;

        drugi = i + 0 + (x - 2) + 0 + i + 0 + (x - 1 - i - 2) + 0;

        if (prvi % 2 == 0) {
            play (i + 1, x - 1);
            play (i + 1, x);
        }
        else {
            play (i + 1, x);
            play (i + 1, x - 1);
        }

    }

    if (x % 2 == 0) par (x);
    else nepar (x);
}

int main () {
    ios_base::sync_with_stdio (false);
    cin.tie (0);

    cin >> n;

    if (n == 1) {
        play (1, 1);
    }
    else if (n == 2) {
        play (1, 1);
    }
    else solve (n);

    cout << rj.size () << "\n";
    for (auto it: rj) cout << it.first << ' ' << it.second << "\n";

    return 0;
}