#include <fstream>

using namespace std;
ifstream f("dame.in");
ofstream g("dame.out");
int n,j,i;
int main()
{
    f>>n;
    if(n==3||n==2) g<<n-1<<"\n";
        else
            g<<n<<"\n";
    if(n==2) g<<1<<" "<<1;
        else
            if(n==3) g<<1<<" "<<1<<"\n"<<2<<" "<<3;
                else
                    if(n%2==0)
                    {   j=n/2;
                        i=1;
                        while(j>=1)
                        {
                            g<<i<<" "<<j<<"\n";
                            i+=2;
                            j-=1;
                        }
                        i=2;
                        j=n;
                        while(i<=n)
                        {
                            g<<i<<" "<<j<<"\n";
                            i+=2;
                            j-=1;
                        }
                    }
                    else
                    {
                        i=1;
                        j=n/2+1;
                        while(j>=1)
                        {
                            g<<i<<" "<<j<<"\n";
                            i+=2;
                            j-=1;
                        }
                        i=2;
                        j=n;
                        while(i<=n-1)
                        {
                            g<<i<<" "<<j<<"\n";
                            i+=2;
                            j-=1;
                        }
                    }
    return 0;
}