#include <iostream>
#include <fstream>
#define input "ciur.in"
#define output "ciur.out"
#define NMAX 2000005
using namespace std;

ifstream fin(input);
ofstream fout(output);

int N;
bool sieve[NMAX];

int main()
{
  int cnt = 0;
  fin >> N;
  for(int i = 2; i <= N ; i++)
  {
    if(!sieve[i])
    {
      cnt++;
      for(int j = i + i ; j <= N ; j += i)
        sieve[j] = 1;
    } 
  }

  fout << cnt << "\n";

  return 0;
}