using namespace std;
#include <fstream>
#define NMAX 1000005
ifstream fin("fractii.in");
ofstream fout("fractii.out");
int N;
char prim[NMAX];
long tot[NMAX];
long long S;
int main(void)
{
    int i, j;
 	fin>>N;
	for(i=1;i<=N;i++)
		tot[i]=i;
  	for (i = 2; i <= N; ++i)
        if (!prim[i])
        {
            tot[i]=i-1;
            for (j = i+i; j <= N; j += i)
				{
				prim[j] = 1;
				tot[j]=tot[j]/i*(i-1);
				}
			
        }
	for(i=1;i<=N;i++)
		S=S+1LL*tot[i];
		
	fout<<2*S-1<<"\n";
    return 0;
}