#include<iostream>
using namespace std;
typedef long long LL;
const int N = 1000010;
int primes[N];
int euler[N];
bool st[N];
int n, cnt;
void get_eulers(int n){
euler[1] = 1;
for(int i = 2; i <= n; i ++){
if(!st[i]) {
primes[cnt ++] = i;
euler[i] = i - 1;
}
for(int j = 0; primes[j] <= n / i; j ++){
int t = primes[j] * i;
st[t] = true;
if(i % primes[j] == 0){
euler[t] = primes[j] * euler[i];
break;
}
euler[t] = euler[i] * (primes[j] - 1); //当 i % prime[j] != 0的情况
}
}
}
int main(){
cin >> n;
LL res = 0;
get_eulers(n);
for(int i = 1; i <= n; i ++){
res += euler[i];
}
cout << res << endl;
return 0;
}