#include <iostream>
#include <fstream>
using namespace std;
ifstream fin("fractii.in");
ofstream fout("fractii.out");
int n, i, j,nr;
int cmmdc(int a,int b)
{
    while(b)
    {
        int r=a%b;
        a=b;
        b=r;
    }
    return a;
}
int main()
{
    fin >> n;
    for(i=1;i<=n;i++)
        for(j=i+1;j<=n;j++)
    {
        if(cmmdc(i,j)==1) cout << i << " " << j <<endl,nr++;
    }
    fout << nr*2+1;
}