#include <bits/stdc++.h>
using namespace std;
const int N = 1e7 + 5;
int n, m, tot, now, pri[N], p[N], phi[N], num[N], sum[N];
long long one, two, three;
int main() {
  scanf("%d", &n);
  phi[1] = 1;
  for (int i = 2; i <= n; i++) {
    if (!p[i]) {
      p[i] = pri[++tot] = i;
      phi[i] = i - 1;
    }
    for (int j = 1; j <= tot; j++) {
      if (i * pri[j] > n) break;
      p[i * pri[j]] = pri[j];
      if (i % pri[j] == 0) {
        phi[i * pri[j]] = phi[i] * pri[j];
        break;
      } else
        phi[i * pri[j]] = phi[i] * (pri[j] - 1);
    }
  }
  for (int i = 2; i <= n; i++) one += i - 1 - phi[i];
  for (int i = 2; i <= n; i++) num[p[i]]++;
  for (int i = 2; i <= n; i++) sum[i] = sum[i - 1] + num[i];
  for (int i = 2; i <= n; i++) two += 1ll * num[i] * sum[n / i];
  for (int i = 2; i <= n; i++)
    if (1ll * p[i] * p[i] <= n) two--;
  two = two / 2 - one;
  m = n - 1;
  for (int i = tot; i >= 1; i--) {
    if (pri[i] * 2 > n)
      m--;
    else
      break;
  }
  three = 1ll * m * (m - 1) / 2 - one - two;
  printf("%I64d\n", one + two * 2 + three * 3);
  return 0;
}
