#include<bits/stdc++.h>
#define ll long long
using namespace std;
int n,cnt,p[1000001],phi[1000001];
ll sum[10000001],ans;
bool flag[10000001];
void f(int n){
	phi[1]=1;
	for(int i=2;i<=n;++i){
		if(!flag[i]){
			p[++cnt]=i;
			phi[i]=i-1;
		}
		for(int j=1;j<=cnt&&i*p[j]<=n;++j){
			flag[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) sum[i]=sum[i-1]+phi[i];
}
int main(){
	freopen("gcd_prime.in","r",stdin);
	freopen("gcd_prime.out","w",stdout);
	cin>>n;
	f(n);
	for(int i=1;i<=cnt;++i) ans+=2*sum[n/p[i]]-1;
	cout<<ans<<endl;
	return 0;
}