#include <bits/stdc++.h>
#define ff first
#define ss second
#define NMAX 1000005
#define pb push_back
using namespace std;
const string file = "fractii";

ifstream fin (file+".in");
ofstream fout (file+".out");
typedef long long ll;
typedef long double ld;

const ll INF = 9223372036854775807ll;
const int dx[] = {1, -1, 0, 0}, dy[] = {0, 0, 1, -1}, inf = 2147483647;
ll N;
ll pd[NMAX];
void solve()
{
    for(ll i=2; i<=N;++i)
        pd[i]=i;
    pd[1]=0;
    for(ll i=2;i<=N;++i)
    {
        if(pd[i] == i)
        {
            for (ll j=i;j<=N;j+=i) {
                pd[j]/=i;
                pd[j]*=(i-1);
            }
        }
    }
}
int main()
{
    fin >> N;
    solve();
    ll Sol = 1;
    for(ll i=2;i<=N;++i)
        Sol += 2*pd[i] ;
    fout << Sol <<"\n";
    return 0;
}