#include <fstream>

using namespace std;

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

int main()
{
    int n;
    in >> n;
    if (n <= 2)
        out << 1 << '\n' << 1 << " " << 1;
    else
    {
        if (n % 2 == 1)
        {
            out << n << '\n';
            int x = 1, y = 1;
            for (int i = 1; i <= n; ++i)
            {
                if (y > n)
                    y = 2;
                out << x << " " << y << '\n';
                ++x;
                y += 2;
            }
        }
        else
        {
            out << n << '\n';
            int x = 1, y = 1, nr = 1;
            for (int i = 1; i <= n - 1; ++i)
            {
                if (y > n)
                    y = 2;
                out << x << " " << y << '\n';
                ++x;
                y += 2;
            }
            out << n << " " << 1;
        }
    }
    return 0;
}