#include<fstream.h>
int main ()
{
int ok;
long n,k=0,i,j;
ifstream f("ciur.in");
ofstream g("ciur.out");
f>>n;
if(n>=2)
{k=1;
for(i=3;i<=n;i=i+2)
 {
 ok=0;
 for(j=3;j<=i/2;j=j+2)
  if(i%j==0)
   ok=1;
 if(ok==0) k++;
 }
g<<k;
f.close();
g.close();
return 0;
}