#include <iostream>
#include <fstream>

using namespace std;
const int Nmax=2000000;
ifstream in("ciur.in");
ofstream out("ciur.out");
bool v[Nmax+1];
int n;
int main()
{
    int k=0;
    in>>n;
   for(int i=2;i<=n;i++)
   {
       if(v[i]==0)
       {


       k++;
       for(int j=i+i;j<=n;j=j+i)
        v[j]=1;

        }
   }
    out<<k;
}