#include <fstream>
using namespace std;
ifstream in("ciur.in");
ofstream out("ciur.out");
long int main()
{
int n,m,i,j,p;
in>>n;
m=2;
for(i=5;i<=n;i=i+2)
                    {p=0;
                        for(j=3;j<=i/2;j++)
                        if(i%j==0)
                                  p=1;
                    if(p==0)
                    m=m+1;}
out<<m;                                        
}