#include <iostream>
#include <vector>
using namespace std;

vector<int> Prime;
void PrimeCalc() {
  bool IsPrime[1000000];
  for(int i=0; i<1000000; i++) {
    IsPrime[i] = true;
  }
  IsPrime[0] = IsPrime[1] = false;
  for (int i=2; i<1000000; i++) {
    if (IsPrime[i]) {
      Prime.push_back(i);
      for (int j=2*i; j<1000000; j+=i) {
        IsPrime[j] = false;
      }
    }
  }
}

void solve() {
  PrimeCalc();
  int n;
  while (cin >> n) {
    int ans = 0;
    for (int i=0; i<Prime.size(); i++) {
      if (Prime[i]<=n) {
        ans++;
      } else {
        break;
      }
    }
    cout << ans << endl;
  }
}

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