#include <fstream>
#define var auto

int main()
{
  int n;
  std::ifstream("ciur.in") >> n;


  var sieve = new bool[n + 1];
  for (var i = 2; i <= n; ++i)
    sieve[i] = true;

  for (var i = 2; i < n; ++i)
    if (sieve[i])
      for (var j = i + i; j <= n; j += i)
        sieve[j] = false;

  var sol = 0;
  for (var i = 2; i <= n; ++i)
    if (sieve[i])
      ++sol;

  std::ofstream("ciur.out") << sol;
}