#include <iostream>
#include <fstream>
using namespace std;
ifstream in("fractii.in");
ofstream out("fractii.out");
const int MAX=1000001;
int fi[MAX],n;
int main()
{
    in>>n;
    for(int i=1;i<=n;i++)
        fi[i]=i;
    for(int i=2;i<=n;++i)
    {
        if(fi[i]==i)
            for(int j=i;j<=n;j=j+i)
            fi[j]-=fi[j]/i;
    }
    long long ans=-1;
    for(int i=1;i<=n;++i)
        ans =ans +2*fi[i];
    out<<ans;
    return 0;
}