#include<fstream>
using namespace std;
int ciur[1000000];
int main()
{
	ifstream fin("fractii.in");
	ofstream fout("fractii.out");
	long long n,i,j,s=0;
	fin>>n;
	for (i=2;i<=n/2;i++)
		if (ciur[i]==0)
		{
			for (j=i*i;j<=n/2;j+=i)
				ciur[j]=1;
			j = n/i-1;
			s += j*(j+1)/2;
		}
	fout<<(n-1)*n+1-2*s;
	fin.close();
	fout.close();
	return 0;
}