#include <cstdio>

using namespace std;

const int N = 2000000 + 5;

int n;
int LastPrime[N];
int Prime[N];

inline int Calculate(int n) {
  int cnt = 0;
  for (int i = 2; i <= n; i++) {
    if (LastPrime[i] == 0) {
      LastPrime[i] = i;
      Prime[++cnt] = i;
    }
    for (int j = 1; j <= cnt && i * Prime[j] <= n && Prime[j] <= LastPrime[i]; j++) {
      LastPrime[i * Prime[j]] = Prime[j];
    }
  }
  return cnt;
}

int main() {
  freopen ("ciur.in", "r", stdin);
  freopen ("ciur.out", "w", stdout);
  int n;
  scanf("%d", &n);
  printf("%d \n", Calculate(n));
  return 0;
}