#include <iostream>
#include <stdlib.h>
#include <fstream>
using namespace std;
ifstream in("dame.in");
ofstream out("dame.out");
int main()
{
    int n, st[1001], i, k, j, ev, ok=1;

    in>>n;

    k=1;
    st[k]=0;

    if(n==1)
        out<<1<<"\n"<<1<<" "<<1;
    if(n==2)
        out<<1<<"\n"<<1<<" "<<1;
    if(n==3)
        out<<2<<"\n"<<1<<" "<<1<<"\n"<<3<<" "<<2;
    if(n>3)
        out<<n<<"\n";


    while(k>0 && ok==1)
    {
        while(st[k]<n && ok==1)
        {
            st[k]++;
            ev=1;

            for(i=1;i<=k-1;i++)
                if(st[k]==st[i] || k-i==abs(st[k]-st[i])) ev=0;

                if(ev==1)
                    if(k==n)
                {
                    for(i=1;i<=n;i++)
                    {
                        for(j=1;j<=n;j++)
                        if(j==st[i]) out<<i<<" "<<j<<"\n";

                    }
                    ok=0;
                    break;
                }
                else
                {
                    k++;
                    st[k]=0;
                }
        }
        k--;
    }


    return 0;
}