#include <iostream.h> 
int N, nr,i,j, v[2000000];
int main() 
{     
      cin>>N;  
      for (i=2;i<=N;i++) v[i]=1; 
      for (i=2;i<=N;i++)   
      if (v[i]) 
      {   
          nr++;             
          for(j=2;j<=N;j++) 
          v[i*j]=0;
      } 
      cout<<nr; 
      system("PAUSE"); return 0;
}