#include <iostream>
#include <algorithm>
#include <string>
#include <vector>
#include <cmath>

static int GetPrimeNumberNum(int maxValue);

int main(void)
{
  int n;
  
  while (std::cin >> n) {
    std::cout << GetPrimeNumberNum(n) << std::endl;
  }
  
  return 0;
}

static int GetPrimeNumberNum(int maxValue)
{
  std::vector<int> searchList;
  std::vector<int> primeList;
  
  for (int i = 2; i <= maxValue; i++) {
    searchList.push_back(i);
  }
  
  double maxValueSq = sqrt((double)maxValue);
  
  while (true) {
    int newPrime = searchList.at(0);
    
    if (newPrime > maxValueSq) {
      break;
    }
    
    primeList.push_back(newPrime);
    
    for (std::vector<int>::iterator it = searchList.begin();
         it != searchList.end();
         ) {
      if (*it % newPrime == 0) {
        it = searchList.erase(it);
      }
      else {
        ++it;
      }
    }
  }
  
  for (std::vector<int>::iterator it = searchList.begin();
       it != searchList.end();
       ++it) {
    primeList.push_back(*it);
  }
  
  searchList.clear();
  
  return primeList.size();
}