#include <iostream>
#include <fstream>
using namespace std;

ifstream fin("ciur.in");
ofstream fout("ciur.out");
const int MAX_SIZE = 2000000;
long long n, ciur[MAX_SIZE + 1];

int eratosthenes_chiur(int n) {
  int counter = 0;
  for (int i = 2; i <= n; ++i) {
    if (ciur[i] == 0) {
      counter++;
      for (int j = i + i; j <= n; j += i) {
        ciur[j] = 1;
      }
    }
  }
  return counter;
}

int main() {
  fin >> n;
  fout << eratosthenes_chiur(n);
  return 0;
}