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