#include<bits/stdc++.h>
using namespace std;
const int N=1e7+5;
int n,a[N],c,p[N];
long long s;
int b[N];
int main(){
	cin>>n;
	for(int i=2;i<=n;i++){
		if(!b[i]){
			a[c++]=i;
			p[i]=i-1;
		}
		for(int j=1;j<=c&&i*a[j]<=n;j++){
			b[i*a[j]]=1;
			if(i%a[j]==0){
				p[i*a[j]]=a[j]*p[i];
				break;
			}
			else{
				p[i*a[j]]=(a[j]-1)*p[i];
			}
		}
	}
	for(int i=1;i<=n;i++){
		p[i]+=p[i-1];
	}
	for(int i=1;i<=c;i++){
		s+=(p[n/a[i]]<<1);
	}
	s+=c;
	cout<<s;
	return 0;
}