#include <bits/stdc++.h>
using namespace std;
template <class T>
inline void gmin(T &x, const T &y) {
  if (x > y) x = y;
}
template <class T>
inline void gmax(T &x, const T &y) {
  if (x < y) x = y;
}
const int BufferSize = 1 << 16;
char buffer[BufferSize], *Bufferhead, *Buffertail;
bool Terminal;
inline char Getchar() {
  if (Bufferhead == Buffertail) {
    int l = fread(buffer, 1, BufferSize, stdin);
    if (!l) {
      Terminal = 1;
      return 0;
    }
    Buffertail = (Bufferhead = buffer) + l;
  }
  return *Bufferhead++;
}
template <class T>
inline bool read(T &x) {
  x = 0;
  char c = Getchar(), rev = 0;
  while (c < '0' || c > '9') {
    rev |= c == '-';
    c = Getchar();
    if (Terminal) return 0;
  }
  while (c >= '0' && c <= '9') x = x * 10 + c - '0', c = Getchar();
  if (c == '.') {
    c = Getchar();
    double t = 0.1;
    while (c >= '0' && c <= '9')
      x = x + (c - '0') * t, c = Getchar(), t = t / 10;
  }
  x = rev ? -x : x;
  return 1;
}
template <class T1, class T2>
inline bool read(T1 &x, T2 &y) {
  return read(x) & read(y);
}
template <class T1, class T2, class T3>
inline bool read(T1 &x, T2 &y, T3 &z) {
  return read(x) & read(y) & read(z);
}
template <class T1, class T2, class T3, class T4>
inline bool read(T1 &x, T2 &y, T3 &z, T4 &w) {
  return read(x) & read(y) & read(z) & read(w);
}
inline bool reads(char *x) {
  char c = Getchar();
  while (c < 33 || c > 126) {
    c = Getchar();
    if (Terminal) return 0;
  }
  while (c >= 33 && c <= 126) (*x++) = c, c = Getchar();
  *x = 0;
  return 1;
}
template <class T>
inline void print(T x, const char c = '\n') {
  if (!x) {
    putchar('0');
    putchar(c);
    return;
  }
  if (x < 0) putchar('-'), x = -x;
  int m = 0, a[20];
  while (x) a[m++] = x % 10, x /= 10;
  while (m--) putchar(a[m] + '0');
  putchar(c);
}
const int inf = 0x3f3f3f3f;
const int N = 10000005, M = 100005, mod = 1e9 + 7;
template <class T, class S>
inline void ch(T &x, const S y) {
  x = (x + y) % mod;
}
inline int exp(int x, int y, const int mod = ::mod) {
  int ans = 1;
  while (y) {
    if (y & 1) ans = (long long)ans * x % mod;
    x = (long long)x * x % mod;
    y >>= 1;
  }
  return ans;
}
int n, m, p[N], c[N], phi[N], sum[N];
bool vis[N];
int main() {
  scanf("%d", &n);
  if (n == 1) {
    puts("0");
    return 0;
  }
  for (int i = 2; i <= n; i++) {
    if (!vis[i]) {
      p[++m] = i;
      phi[i] = i - 1, c[m]++;
    }
    for (int j = 1; j <= m && p[j] * i <= n; j++) {
      vis[p[j] * i] = 1;
      c[j]++;
      if (i % p[j] == 0) {
        phi[i * p[j]] = phi[i] * p[j];
        break;
      }
      phi[i * p[j]] = phi[i] * (p[j] - 1);
    }
  }
  long long ans = (long long)(n - 1) * (n - 1) * 3;
  for (int i = 1; i <= m; i++) sum[i] = sum[i - 1] + c[i];
  for (int i = m, j = 0; i; i--) {
    while (j < m && (long long)p[j + 1] * p[i] <= n) j++;
    ans -= (long long)c[i] * sum[j];
    if ((long long)p[i] * p[i] > n) ans -= (long long)c[i] * c[i];
  }
  long long ss = 1;
  for (int i = 2; i <= n; i++) ss += phi[i];
  ss = ss * 2 - 1;
  ans -= (long long)n * n - ss;
  int cnt = 0;
  for (int i = 1; i <= m; i++)
    if (p[i] * 2 > n) cnt++;
  ans -= 3ll * ((long long)cnt * (n - 2) * 2 - (long long)cnt * (cnt - 1));
  for (int i = 2; i <= n; i++) ans--;
  cerr << "ans"
       << "=" << ans << endl;
  cout << ans / 2 << endl;
  return 0;
}
