#include <iostream>
#include <cstdio>

using namespace std;

const int NMAX = 2000000;

bool ciur[NMAX + 5];

int main() {
  freopen("ciur.in", "r", stdin);
  freopen("ciur.out", "w", stdout);
  int n, ans = 0;

  scanf("%d", &n);

  ciur[0] = ciur[1] = true;
  for(int i = 2; i <= n; i++)
    if(!ciur[i]) {
      ans++;
      for(int j = 2 * i; j <= n; j += i)
        ciur[j] = true;
    }
  printf("%d", ans);

  return 0;
}