#include <fstream>
using namespace std;

int n, sol[1010];

inline void swap(int &a, int &b)
{
    int x = a;
    a = b;
    b = x;
}

int main()
{
    ifstream f("dame.in");
    ofstream g("dame.out");

    f >> n;
    for (int i = 2; i <= n; i += 2)
        sol[++sol[0]] = i;

    if (n % 12 == 3 || n % 12 == 9)
        sol[1] = 0, sol[++sol[0]] = 2;

    for (int i = 1; i <= n; i += 2)
        sol[++sol[0]] = i;

    if (n % 12 == 8)
    {
        int i;
        for (i = 1; sol[i] % 2 == 0; ++i);
        for (; i <= sol[0]; i += 2)
            swap(sol[i], sol[i + 1]);
    }
    if (n % 12 == 2)
    {
        int i;
        for (i = 1; sol[i] % 2 == 0; ++i);
        swap(sol[i], sol[i + 1]);
        sol[i + 2] = 0;
        sol[++sol[0]] = 5;
    }
    if (n % 12 == 3 || n % 12 == 9)
    {
        int i;
        for (i = 1; sol[i] % 2 == 0; ++i);
        sol[i] = sol[i + 1] = 0;
        sol[++sol[0]] = 1;
        sol[++sol[0]] = 3;
    }

    int nr = 1;
    if (n == 1) g << "1\n1 1\n";
    else
    if (n == 2)
    {
        g << "1\n1 1";
    }
    else
    if (n == 3)
    {
        g << "2\n1 1\n2 3";
    }
    else
    {
        g << n << '\n';
        for (int i = 1; i <= sol[0] && nr <= n; ++i)
        {
            while (sol[i] == 0) ++i;
            g << nr << ' ' << sol[i] << '\n';
            ++nr;
        }
    }
    g.close();
    return 0;
}