#include<fstream.h>   
int n,cnt;   
char prim[2000005];   
  
int main()   
{   
 int i,j;   
 ifstream fin("ciur.in");   
 ofstream fout("ciur.out");   
 fin>>n;   
  for(i=2;i<=n;++i)   
   prim[i]=1;   
  for(i=2;i<=n;++i)   
    if(prim[i])   
       {   
      ++cnt;   
      for(j=i+i;j<=n;j+=i)   
         prim[j] = 0;   
       }   
   fout<<cnt<<"\n";   
return 0;   
}  
#include<fstream.h>
int n,cnt;
char prim[2000005];

int main()
{
 int i,j;
 ifstream fin("ciur.in");
 ofstream fout("ciur.out");
 fin>>n;
  for(i=2;i<=n;++i)
   prim[i]=1;
  for(i=2;i<=n;++i)
    if(prim[i])
       {
	  ++cnt;
	  for(j=i+i;j<=n;j+=i)
		 prim[j] = 0;
       }
   fout<<cnt<<"\n";
return 0;
}