#include<fstream>
#include<math.h>
using namespace std;
int main()
{
    ifstream fin("ciur.in");
    ofstream fout("ciur.out");
    int n,i,j,nrprime=1;
    bool prim=true;
    fin>>n;
    for(i = 3; i <= n; i+=2)
    {
       prim = true;
       for(j = 3; j <= sqrt(i); j+=2)
                    if(i % j ==0)
                    {
                        prim = false;
                        break;
                    }
       if(prim)
            nrprime++;
    }
    fout << nrprime;
}