#include <iostream>
#include <fstream>
#include <cmath>
using namespace std;

int main()
{   ifstream cin("fractii.in");
    ofstream cout("fractii.out");
    int n,x=0,i,j;
    cin>>n;
    for (i=2; i<=n; i++)
    for (j=2; j<=n; j++)
    {
        int t=0;
        for (int d=2; d<=i/2; d++) if (i%d==0 && j%d==0) {t=1; break;}
        if (t==0 && i%j!=0 && j%i!=0) {x++; cout<<i<<" "<<j<<endl;}
    }
    cout<<x+2*n-1;
    return 0;
}