#include <iostream>
#include <fstream>
using namespace std;
int prim(int x)
{
    int d;
    for(d=2;d<=x/2;d++)
        if(x%d==0)
        return 0;
    return 1;
}
int main()
{
    ifstream in("fractii.in");
    ofstream out("fractii.out");
    int n,i,j,nr=1;
    in>>n;
    i=1;
    while(i<=n)
    {
        j=1;
        while(j<=n)
            {
            if(i!=j and prim(i) and prim(j))
           {
               cout<<i<<" "<<j<<endl;
                nr++;
           }
           j++;
            }
           i++;
    }
    out<<nr;

    return 0;
}