#include <fstream>
#define nmax 1000000

using namespace std;
ifstream f("fractii.in");
ofstream g("fractii.out");
int N, v[nmax];
long long nrFrc;
int main()
{int i, j, nrMult, jum;
    f>>N;
    nrFrc = N * (N - 1) + 1;
    jum = N / 2 + 1;
    for(i = 2; i <= jum; ++i){
        nrMult = 0;
        if(!v[i]){
            for(j = i + i; j <= N; j += i){
                nrFrc -= 2;
                ++nrMult;
                v[j] = true;
            }
            nrFrc -= nrMult * (nrMult - 1);
        }
    }
    g<<nrFrc << '\n';
    return 0;
}