#include <bits/stdc++.h>
#define NMAX 2000005
using namespace std;

ifstream f("ciur.in");
ofstream g("ciur.out");

int n, k;
long long i, j;
bool nprim[NMAX];
vector <int> pr;

void ciur() {
  for (i = 2; i <= NMAX; i++)
    if (nprim[i] == false) {
      for (j = i*i; j <= NMAX; j += i)
         nprim[j] = true;
      pr.push_back(i);
    }
}

int main() {

  f >> n;
  k = 0;
  ciur();

  for (i = 0; pr[i] <= n; i++)
      k += 1;

  g << k;

 return 0;
}