#include<fstream.h>
int n,cnt;
char prim[2000005];

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