#include <stdio.h>
const int MAX_V = 1000000;
int prime[MAX_V + 1];
int sum[MAX_V + 1];
int main() {
  int i, k, v, n, max = 0;
  for(i = 2; i <= MAX_V; i++) {
    prime[i] = 1;
  }
  for(i = 2; i*i <= MAX_V; i++) {
    if(prime[i]){
      for(k = 2 * i; k <= MAX_V; k += i) {
        prime[k] = 0;
      }
    }
  }
  while(scanf("%d", &n) != EOF){
    for(i = 2;i <= n;i++){
      sum[n] += prime[i];
    }
  printf("%d\n", sum[n]);
  }
  return 0;
}