#include<fstream.h>
int main ()
{
int ok;
long n,k=0,i,j;
ifstream f("ciur2.in");
ofstream g("ciur2.out");
f>>n;
for(i=2;i<=n;i++)
 ok=0;
 for(j=2;j<=i-1;j++)
  if(i%j==0)
   ok=1;
 if(ok==0) k++;
f.close();
g.close();
return 0;
}