#include<fstream.h>
#define dim 2000004
char ciur[dim];
int n,k,i,j;
ifstream f("ciur.in");
ofstream g("ciur.out");
int main()
{
 f>>n;
for ( i=2;i<=n;++i)
	ciur[i]=1;

for (i=2;i<=n;++i)
	if (ciur[i])
	 for ( j=2;j<=n/i;++j)
	   ciur[i*j] = 0;

for(i=2;i<=n;i++)
    if(ciur[i])
     k++;

     g<<k;

   f.close();
   g.close();
   return 0;
}