#include <fstream>
#include <cmath>

using namespace std;

bool compuse[2000001];
int n, d, m, prime;
ifstream fi("ciur.in");
ofstream fo("ciur.out");

int main () {
  fi >> n;
  for (d = 2; d <= n; d++)
    if (not compuse[d]) {
      for (m = d * d; m <= n; m += d)
        compuse[m] = true;
      prime++;
    }
  fo << prime;
  return 0;
}