#include <iostream>
#include <fstream>
using namespace std;
ifstream fin ("ciur.in");
ofstream fout ("ciur.out");
int N, cnt;
char prim[2000005];
int main(void) {
  int i, j;
  fin >> N;
  for (i = 2; i <= N; ++i)
      prim[i] = 1;
  for (i = 2; i <= N; ++i)
      if (prim[i]) {
          ++cnt;
          for (j = i+i; j <= N; j += i)
              prim[j] = 0;
      }

  fout << cnt;
  fin.close();
  fout.close();
  return 0;
}