#include <fstream>

using namespace std;
ifstream f("fractii.in");
ofstream g("fractii.out");
unsigned long long n,i,j,op,v[10000001];
int main()
{
    f>>n;
    op=n*n;
    for(i=2; i<=n; i++)
    {
        if(v[i]==0)
        {
            v[i]=1;
            for(j=n/i;j>1;j=j--)
            {
                op=op-2*j+1;
            }
            op=op-1;
            for(j=i*2;j<=n;j=j+i)
            {
                if(v[j]==1)
                {
                    op++;
                }
                v[j]=1;
            }
        }
    }
    g<<op<<'\n';
    return 0;
}