#include <iostream>
#include <fstream>
#include <vector>
#include <cstring>
#include <set>

using namespace std;
#define oo 0x3f3f3f3f
#define cost first 
#define ngh second 

ifstream f("ciur.in");
ofstream g("ciur.out");
int n;
bitset<2000001> viz;

void solve() {
  f>>n;
  int count = 0;
  for(int i = 2;i <= n;++i) {
    if(!viz[i]) {
      ++count;
      for(int j = i;j <= n;j += i) {
        viz[j] = 1;
      }
    }
  }

  g<<count;
}

int main() {
  solve();
  return 0;
}