#include <fstream.h>
#include <math.h>
ifstream f("ciur.in");
ofstream g("ciur.out");
long v[2000000], n, i, s=1;

void delete(long k)
	{
   int d=2;
   while (t<=n)
   	{
      v[k*d]=0;
      d++;
      }
   }


int main()
	{
   f>>n;
   for (i=2;i<=n;i++)
   	v[i]=1;
   delete(2);
   for (i=3;i<=sqrt(n);i=i+2)
   	if (v[i])
      	{
         s++;
      	delete(i);
         }
   g<<s;
   f.close();
   g.close();
   return 0;
   }