#include <fstream>
#include <bitset>
//#include <iostream>
using namespace std;
ifstream in("ciur.in");
ofstream out("ciur.out");
bitset<2000001> prim;
int n,d,m,prime=0;

int main()
{
   in>>n;
   prim.set();
   for(d=1;d<=n;d++)
   if(prim[d])
   {
       if(n/d>=d)
       for(m=d*d;m<=n;m+=d)
                prim[m]=0;
       prime++;

   }
   out<<prime;
    return 0;
}