#include <fstream>
using namespace std;
bool v[1000000];
int main()
{
	ifstream f("fractii.in");
	ofstream o("fractii.out");
	int n,i,k,nr;
	f>>n;
	nr=2*n-1;
	for (k=2;k<n;k++)
	{
		for (i=k;i<=n;i++)
			v[i]=1;
		for (int s=2;s<=k;s++)
		{
			if (k%s==0)
				for (i=s;i<=n;i+=s)
					v[i]=0;
		}
		for (i=k;i<=n;i++)
			{
				if (v[i]) nr+=2;
		    }
	}    
	o<<nr;
	return 0;
}