#include <fstream>

using namespace std;

fstream f;
fstream g;

int n;
int i,j;
long sum;
int a[1000001][2];
int k;

int main()
{
    f.open("fractii.in",fstream::in);
    f >> n;
	sum=2*n-1;
	g.open("fractii.out",fstream::out);
	for(i=2;i<=n;i++)
	{
	   if(a[i][1]==0){
		     sum++;
			 for(j=2*i;j<=n;j+=i)
				 a[i][1]++;
	   }
    }
	f.close();

    
    g << sum << "\n";
    g.close();	
	
	return 0;
}