#include <bits/stdc++.h>
using namespace std;

ifstream fin("fractii.in");
ofstream fout("fractii.out");

int n, i, j, vec[1000001];
int64_t cnt = 1;
int main(){

    for(i = 1; i <= 1000000; i++) vec[i] = i;
    for(i = 2; i <= 1000000; i++){
        if(vec[i] == i){
            vec[i]--; 
            for(j = 2; j * i <= 1000000; j++)
                vec[i*j] = vec[i*j] / i * (i - 1);
        }
    }

    fin >> n;
    for(i = n; i >= 2; i--) cnt += 2* vec[i];
    fout << cnt;
   
}