#include <fstream>
#include <iostream>
using namespace std;
ifstream fin("ciur.in");
ofstream fout("ciur.out");
int n, cnt;
bool c[2000005];
void ciur() {
  c[0] = 1, c[1] = 1;
  for (int i = 4; i <= n; i += 2)
    c[i] = 1;
  for (int i = 3; i * i <= n; i++)
    if (c[i] == 0)
      for (int j = i; i * j <= n; j += 2)
        c[i * j] = 1;
}
int main() {
  fin >> n;
  ciur();
  for (int i = 1; i <= n; i++)
    if (!c[i])
      cnt++;
  fout << cnt;
  return 0;
}