#include <fstream>

using namespace std;

ifstream in("dame.in");
ofstream out("dame.out");

int v[1001];

int main()
{
    int n, k = 0, kpar;
    in >> n;
    if (n % 12 == 3 || n % 12 == 9)
    {
        for (int i = 4; i <= n; i += 2)
            v[++k] = i;
        v[++k] = 2;
    }
    else
    {
        for (int i = 2; i <= n; i += 2)
            v[++k] = i;
    }
    kpar = k + 1;
    for (int i = 1; i <= n; i += 2)
        v[++k] = i;
    if (n % 12 == 8)
    {
        for (int i = kpar; i <= k; i += 2)
            swap(v[i], v[i + 1]);
    }
    if (n % 12 == 2)
    {
        swap(v[kpar], v[kpar + 1]);
        for (int i = kpar + 2; i < k; ++i)
            v[i] = v[i + 1];
        v[k] = 5;
    }
    if (n % 12 == 3)
    {
        for (int i = kpar; i < k - 1; ++i)
            v[i] = v[i + 2];
        v[k - 1] = 1;
        v[k] = 3;
    }
    out << n << '\n';
    for (int i = 1; i <= n; ++i)
        out << i << " " << v[i] << '\n';
    return 0;
}