#include <iostream>
#include <fstream>
using namespace std;
ifstream fin("ciur.in");
ofstream fout("ciur.out");

int n, ans;
bool a[2000000];
int ciur() {
  for (int i = 2; i <= n; i++) {
    if (!a[i]) {
      ans++;
      for (int j = i + i; j <= n; j += i)
        a[j] = true;
    }
  }
  return ans;
}

int main(int argc, const char * argv[]) {
  fin >> n;
  fout << ciur();
}