#pragma GCC optimize("O3")
#include<bits/stdc++.h>
using namespace std;
#define rc(x) return cout<<x<<endl,0
#define pb push_back
#define dbg(x) cout << #x << '=' << x << '\n';
#define ll long long
#define sz size()
#define x first
#define y second
#define pi pair <int, int>
#define pii pair <pi, pi>
#define vi vector <int>
const ll mod = 1e9 + 7;
ll ans;
int s[1000001];
int n;
ll cnt;

int gcd(int x, int y){
    if(x==1 || y==1) return 1;
    if(x==0) return y;
    if(y==0) return x;
    return gcd(y%x, x);
}

int32_t main(){
    ios_base :: sync_with_stdio(0); cin.tie(); cout.tie();
    ifstream cin("fractii.in");
    ofstream cout("fractii.out");
    cin>>n;
    for(int i=1; i<=n; i++) s[i]=i;
    for(int i=2; i<=n; i++){
        if(s[i]==i){
            for(int j=i; j<=n; j+=i){
                s[j]=s[j]/i *(i-1);
            }
        }
    }
    for(int i=1; i<=n; i++){
        ans+=2LL*s[i];
    }
    ans--;
    /* for(int i=n; i>=2; i--){
        cnt=0;
        ans+=i-1;
        if(sqrt(i-1)*sqrt(i-1)==i-1) cnt--;
        for(int j=sqrt(i-1); j>=1; j--){
            if(gcd(i, j)!=1) cnt+=1LL*2;
        }
    ans-=cnt;
    } */
    cout<<ans;
}