#include <iostream>
#include <fstream>
using namespace std;
bool v[1000001];
int cmmdc(int a, int b)
{
    int t;
    while (b != 0)
    {
        t = b;
        b = a % b;
        a = t;
    }
    return a;
}
int main()
{
    ifstream f("fractii.in");
    ofstream g("fractii.out");
    int i,j,n,s,d;
    f>>n;
    for(i=2;i<=n;i++)
    {
        if(v[i]==0)
            for(j=2;j*i<=n;j++)
            v[i*j]=1;
    }
    s=4;
    for(i=2;i<=n;i++)
        {
            for(j=1;j<=n;j++)
                if(v[j]==0||v[i]==0)
               if(cmmdc(i,j)==1)
               {
                   g<<i<<"/"<<j<<endl;
                   s++;
               }
        }
        g<<s;
    return 0;
}