#include <fstream>
#include <vector>

using namespace std;

ifstream cin ("ciur.in");
ofstream cout ("ciur.out");

int cnt, n;

int low[2000005];
vector <int> primes;

int main() {
  cin >> n;
  for(int i = 2; i <= n; i++) {
    if(low[i] == 0) {
      low[i] = i;
      primes.push_back(i);
    }
    for(int j = 0; j < primes.size() && primes[j] <= low[i] && i * primes[j] <= n; j++)
      low[i * primes[j]] = primes[i];
  }
  cout << primes.size();
  return 0;
}