#include <iostream>
#include <fstream>
using namespace std;
ifstream in("ciur.in");
ofstream out("ciur.out");
int main()
{
    int n,i,p,cont=0,j,ok;
    in>>n;
    for(i=2;i<=n;i++)
    {
          ok=1;
          for(j=2;j*j<=i;j++&& ok==1)
          {
                if(i%j==0)
                {
                      ok=0;
                }

          }
          if(ok==1) cont++;


    }
    out<<cont;
    return 0;
}