#include <fstream.h>   
ifstream f("ciur.in");
ofstream g("ciur.out");   
int main()
{char a[2000002];
 long n,i,j,k=0;      
 f>>n;  
 for (i=2;i<=n;i++) a[i]=1;   
 for (i=2;i<=n;i++)   
     if (p[i])    
      for (j=2;i*j<=n;j++) 
        p[i*j]=0;      
 for (i=2;i<=n;i++) if (p[i]) k++;   
 g<<k;   
 f.close();
 g.close();   
 return 0;   
}