#include <iostream>
#include <fstream>
using namespace std;
long long n;
bool v[1000000];

long long ciur()
{
    int i,j;
    for (i=4;i<=n;i=i+2)
        v[i]=1;
    long long n2=n*n;
    for (i=3;i*i<=n;i=i+2)
    {
        if (v[i]==0)
        {
            for (j=i*i;j<=n;j=j+i*2)
            {
                v[j]=1;
            }
        }
    }
    for (i=2;i<=n;i++)
    {
        if (v[i]==0)
            n2=n2-((n/i)*(n/i))+n/i;
    }
    return n2-n+1;
}
int main()
{
    ifstream in("fractii.in");
    ofstream out("fractii.out");
    in>>n;
    out<<ciur();
    out.close();
    in.close();
    return 0;

}