#include<fstream>
#define DIM 1000005
using namespace std;
int n, i, j, p, a;
long long sum, t[DIM];
int c[DIM], pr[DIM];
ifstream fin("fractii.in");
ofstream fout("fractii.out");
int main(){
    fin>> n;
    for(i = 2; i <= n; i++){
        if(c[i] == 0){
            for(j = i + i; j <= n; j+= i){
                c[j] = 1;
                pr[j] = i;
            }
        }
    }
    for(i = 2; i <= n; i++){
        if(c[i] == 0){
            t[i] = i - 1;
            sum += t[i];
            continue;
        }
        a = i;
        p = 1;
        while(a % pr[i] == 0){
            a /= pr[i];
            p *= pr[i];
        }
        if(a == 1){
            t[i] = (pr[i] - 1) * 1LL * (p / pr[i]);
        }
        else{
            t[i] = t[p] * t[a];
        }
        sum += t[i];
    }
    sum = 2 * sum + 1;
    fout<< sum <<"\n";
    return 0;
}