#include <bits/stdc++.h>

using namespace std;

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

const int NMAX(1005);

int main()
{
    int n;
    fin >> n;
    if (n <= 2)
    {
        fout << 1 << '\n' << 1 << " " << 1;
        return 0;
    }
    if (n == 3)
    {
        fout << 2 << '\n' << 1 << " " << 1 << '\n' << 2 << " " << 3;
        return 0;
    }
    vector<int> vec;
    vec.push_back(0);
    if(n % 12 == 3 || n % 12 == 9)
    {
        for(int i = 4; i <= n; i += 2)
            vec.push_back(i);
        vec.push_back(2);
    }
    else
    {
        for(int i = 2; i <= n; i += 2)
            vec.push_back(i);
    }
    int aux = vec.size();
    for(int i = 1; i <= n; i += 2)
        vec.push_back(i);
    if(n % 12 == 8){
        for(int i = aux; i <= n; i += 2)
            swap(vec[i], vec[i + 1]);
    }
    if(n % 12 == 2){
        swap(vec[aux], vec[aux + 1]);
        for(int i = aux + 2; i < n; ++i)
            vec[i] = vec[i + 1];
        vec[n] = 5;
    }
    if(n % 12 == 3 || n % 12 == 9){
        for(int i = aux; i < n - 1; ++i)
            vec[i] = vec[i + 2];
        vec[n - 1] = 1;
        vec[n] = 3;
    }
    fout << n << '\n';
    for(int i = 1; i <= n; ++i)
        fout << i << ' ' << vec[i] << '\n';
    return 0;
}