#include <stdio.h>
 int phi[1000000],n,sol;
 int  phii(int N) {
  int i,j;
for ( i = 1; i <= N; ++i)
    phi[i] = i-1;
for ( i = 2; i <= N; ++i)
    for ( j = 2*i; j <= N; j += i)
        phi[j] -= phi[i];
}

int main() {
freopen("fractii.in","r",stdin);
freopen("fractii.out","w",stdout);
  fscanf("%d",&n);
phii(n);
for (i=2;i<=n;i++)
	sol+=2*phii[i];
fprintf("%d",sol);
return 0;
 }