#include <iostream>
#include <fstream>
#include <unordered_map>
#include <queue>
#include <stack>
#include <vector>

#define ll long long
#define ull unsigned long long
#define pb push_back
using namespace std;
ifstream in("fractii.in");
ofstream out("fractii.out");

const int NMax = 1e6 + 5;
const int inf = 1e9 + 5;

int N;
int prime[NMax],phi[NMax];
bool notPrime[NMax];

int main() {
    in>>N;

    for (int i=4;i <= N;i += 2) {
        notPrime[i] = true;
        prime[i] = 2;
    }

    for (int i=3;i <= N;i += 2) {
        if (notPrime[i]) {
            continue;
        }

        for (int j=3*i;j <= N;j += 2*i) {
            notPrime[j] = true;
            prime[j] = i;
        }
    }

    ll ans = 0;
    for (int i=2;i <= N;++i) {
        if (!notPrime[i]) {
            phi[i] = i-1;
            ans += phi[i];
        }
        else {
            int pw = 1,p = prime[i],aux = i;
            while (aux % p == 0) {
                aux /= p;
                pw *= p;
            }

            if (pw == i) {
                phi[i] = i * (p-1) / p;
            }
            else {
                phi[i] = phi[pw] * phi[i/pw];
            }
            ans += phi[i];
        }
    }

    /*
    for (int i=1;i <= N;++i) {
        out<<i<<' '<<notPrime[i]<<' '<<notPrime[i]<<'\n';
    }
    //*/

    /*
    for (int i=1;i <= N;++i) {
        out<<i<<' '<<phi[i]<<'\n';
    }
    //*/

    out<<ans*2 + 1<<'\n';

    in.close();out.close();
    return 0;
}