#include <iostream>
#include <fstream>
using namespace std;
ifstream fin ("ciur.in");
ofstream fout ("ciur.out");
int n, i, j, raspuns;
char prim[20000002];
int main()
{
  fin>>n;
  for (i=2; i<=n; i++)
    if(prim[i]==0)
  {
      raspuns++;
      for(j=2*i;j<=n;j+=i)
        {
        prim [j]=1;
        }
  }
  fout<<raspuns;
  return 0;
}