#include <bits/stdc++.h>
using namespace std;
#ifdef LOCAL
  #include "settings/debug.cpp"
#else
  #define Debug(...) void(0)
#endif
#define rep(i, n) for (int i = 0; i < (n); ++i)
using ll = long long;
using ull = unsigned long long;

int main() {
  cin.tie(nullptr)->sync_with_stdio(false);
  int n;
  cin >> n;
  if (n == 1) {
    cout << 0 << '\n';
    return 0;
  }
  vector<bool> is_prime(n + 1, true);
  set<int> primes;
  is_prime[0] = is_prime[1] = false;
  for (ll i = 2; i <= n; ++i) {
    if (is_prime[i]) {
      primes.insert(i);
      for (ll j = i * i; j <= n; j += i) is_prime[j] = false;
    }
  }
  int ans = -1;
  for (ll x : primes) {
    if (x * x - 2 <= n && primes.contains(x * x - 2)) ans += 2;
  }
  cout << ans << '\n';
  return 0;
}