#include<fstream>
#include<string>
using namespace std;
long ok[2000000],n,k;
int i,j;
int main()
{
ifstream in("ciur.in")
ofstream out("ciur.out")
in>>n;
k=0;
memset(ok,1,sizeof(ok));
for(i=2;i*i<=n;i++)
  if(ok[i])
   {
    j=2;
    while(i*j<=n)
     {
      ok[i*j]=0;
      j++;
      }
    }
for(i=2;i<=n;i++)
 if(ok[i]) k++;
out<<k;
in.close();
out.close();
return 0;
}