#include <iostream>
using namespace std;

#define NMAX 1000001

int n, prim[NMAX];
void solve(void){
    n=NMAX;
    for (int i=1; i<=n; ++i){
        prim[i]=i;
    }
    for (int i=2; i<=n; ++i){
        if (prim[i]==i) {
            for (int j=i; j<=n; j+=i) {
                prim[j]/=i;
                prim[j]*=(i-1);
            }
        }
    }
    int n;
    cin>>n;
    int sum=0;
    for (int i=1; i<=n; ++i){
        sum+=prim[i]*2;
    }
    cout<<sum-1;
}
int main(void){
    ios::sync_with_stdio(false);
    cin.tie(NULL);
    cout.tie(NULL);
    #ifdef LOCAL
        freopen("date.in", "r", stdin);
    #else
        freopen("fractii.in", "r", stdin);
        freopen("fractii.out", "w", stdout);
    #endif
    solve();
    return 0;
}