#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
const int N=1e7+5;
ll n,f[N],p[N],phi[N],s[N],cnt;
ll ans;
void judge (int n) {
	phi[1]=1;
	for (int i=2;i<=n;i++) {
		if (!f[i]) p[++cnt]=i,phi[i]=i-1;
	    for (int j=1;j<=cnt&&i*p[j]<=n;j++) {
	    	f[i*p[j]]=1;
	    	if (i%p[j]==0) {
				phi[i*p[j]]=phi[i]*p[j];
				break;
			}else{
				phi[i*p[j]]=phi[i]*phi[p[j]];
			}
		}
	}
	for (int i=1;i<=n;i++) s[i]=s[i-1]+phi[i];
} 
int main () {
	freopen("gcd_prime.in","r",stdin);
	freopen("gcd_prime.out","w",stdout);
	cin >> n;
	judge(n);
	for (int i=1;i<=cnt;i++) {
		ans+=2*s[n/p[i]]-1;
	}
	cout << ans <<endl;
	return 0;
}