# include <fstream>
using namespace std;
 char ciur[20000001] ;
int main ()
{
int i,j, nr=0,n;

 ifstream f("ciur.in");
 ofstream g("ciur.out");
 f>>n;
 
 for (i=2;i<=n;i++)
 {if(ciur[i]==0)
 nr++;
for (j=i+i;j<=n;j+=i)
ciur[j]=1;
}
g<<nr;
f.close();
g.close();
return 0;
}