#include <iostream>
#include<math.h>
#include<fstream>
using namespace std;
ifstream f("ciur.in");
ofstream g("ciur.out");
//class PrimeNumbersSieve1

int p[100000];
//p[i] == 0 if i is prime
 int getTheNumber(int n) {
  int i, j, nr = 0;
  for (i = 2; i <= n; ++i) {
    if (p[i] == 0) {
      nr++;
      for (j = i + i; j <= n; j += i) {
        p[j] = 1;
      }
    }
  }
  return nr;
}
int main()
{
    int n;
    f>>n;
    g<<getTheNumber(n);
    return 0;
}