#include <iostream.h>
#include <fstream.h>

#define IN "ciur.in"
#define OUT "ciur.out"

ifstream fin(IN);
ofstream fout(OUT);

int n, cnt;
char prim[2000005];

int main(void)
{
 int i, j;

 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<<endl;
 
 fout.close();
 fin.close();
  
return 0;
}