#include <fstream>

using namespace std;

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

int n;

void solve()
{
    int ind=1,j=1;
    cout<<n<<'\n';
    while(ind<=n)
    {
        while(j<=n)
        {
            cout<<ind<<" "<<j<<'\n';
            ind++;
            j+=2;
        }
        j=2;
        while(j<=n)
        {
            cout<<ind<<" "<<j<<'\n';
            ind++;
            j+=2;
        }
    }
}

int main()
{
    cin>>n;
    if(n==1)
        cout<<"1\n 1 1";
    else if(n==2)
        cout<<"1\n 1 1";
    else if(n==3)
        cout<<"2\n 1 1\n 2 3";
    else if(n==4)
        cout<<"4\n 1 2\n 2 4\n 3 1\n 4 3";
    else
        solve();
    return 0;
}