#include <cstdio>
#include <vector>

using namespace std;

int main() {
  freopen("ciur.in", "r", stdin);
  freopen("ciur.out", "w", stdout);
  int n;
  scanf("%d", &n);
  vector <bool> Prime(n + 1);
  for (int i = 2; i <= n; i++) {
    Prime[i] = 1;
  }
  for (int i = 2; i * i <= n; i++) {
    if (Prime[i] == 1) {
      for (int j = i * i; j <= n; j += i) {
        Prime[j] = 0;
      }
    }
  }
  int ans = 0;
  for (int i = 1 ; i <= n; i++) {
    ans += Prime[i];
  }
  printf("%d \n",ans);
  return 0;
}