#include <bits/stdc++.h> //Andrei Alexandru a.k.a Sho
#define ll long long
#define double long double
#pragma GCC optimize("O3")
#pragma GCC optimize("Ofast")
#define aint(a) (a).begin(), (a).end()
#define f first
#define s second
#define pb push_back
#define mp make_pair
#define pi pair
#define rc(s) return cout<<s,0
#define endl '\n'
#define mod 1000000007ll
#define PI 3.14159265359
#define INF 1000000005
#define LINF 1000000000000000005ll
#define CODE_START  ios_base::sync_with_stdio(false);cin.tie(0);cout.tie(0);
using namespace std;
ll n,cnt[1000005];
map<ll,ll>viz;
int32_t main(){
CODE_START;
ifstream cin("fractii.in");
ofstream cout("fractii.out");
cin>>n;
ll ans=1;
for(ll i=2;i<=n;i++)
{
cnt[i]=i;
}
for(ll i=2;i<=n;i++)
{
    if(cnt[i]==i){
cnt[i]=i-1;
for(ll j=2*i;j<=n;j+=i){
cnt[j]=cnt[j]/i*(i-1);
}
    }
}
for(ll i=2;i<=n;i++)
{
    ans+=cnt[i]*2;
}
cout<<ans<<endl;
}