//Ciurul lui Eratosthenes

#include <fstream>

std::ifstream in("ciur.in");
std::ofstream out("ciur.out");

bool prim[2000000];

int main ()
{
    long i,j,k=1;
    long n;
    in>>n;
    for(i=3;i<=n;i+=2)
    {
                         if(prim[i]==0)
                         {
                                       k++;
                                       for(j=i+i+i;j<=n;j+=i<<1)
                                           prim[j]=1;
                         }
    }
    out<<k;
}