#include <iostream>
#include <cmath>
#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 <= sqrt(n); i++) {
    if (!a[i]) {
      for (int j = 2; j <= n / 2; j++)
        a[i * j] = true;
    }
  }
  for (int i = 2; i <= n; i++)
    if (!a[i])
      ans++;
  return ans;
}

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