#include <fstream>

using namespace std;
ifstream f("fractii.in");
ofstream g("fractii.out");
#define MAXN 1000001
long long int phi[1000001];
void phi1(int x)
{

    for(int i = 1; i <= x; i++)
        phi[ i ] = i;

    for(int i = 2; i <= x; i++)
        if( phi[ i ] == i )
            for(int j = i; j <= x; j += i)
                phi[ j ] = phi[ j ]/i*( i - 1 );
}
int main()
{
    int n;

f>>n;
phi1(n);

long long int s=1;
for(int i=2;i<=n;i++)
    s+=2*phi[i];
g<<s;
}