#include <cstdio>
#define MAX 1000000
#define SQRT 1000
#define TRUE 1
#define FALSE 0
using namespace std;

int is_prime[MAX];
int prime_count[MAX];

void solve() {
  int cnt = 0;
  for (int i = 0; i < MAX; i++) {
    is_prime[i] = TRUE;
  }
  is_prime[0] = is_prime[1] = 0;
  for (int i = 2; i < MAX; ++i) {
    if (is_prime[i] == TRUE) {
      if (i < SQRT) {
        for (int j = i * i; j < MAX; j += i) {
          is_prime[j] = FALSE;
        }
      }
      cnt++;
    }
    prime_count[i] = cnt;
  }
}

int main() {
  solve();
  int n;
  while (~scanf("%d", &n)) {
    printf("%d\n", prime_count[n]);
  }
}
