#include <fstream.h>  
   
 ifstream f("ciur.in");  
 ofstream g("ciur.out");  
   
 long n,nr; 
 char c[2000001];

 void ciur()  
 {  
      long i,j;  
      for (i=2;i<=n;i++)  
        if (c[i]==0)  
          for (j=i+i;j<=n;j=j+i)  
           if (j%i==0)  
             c[j]=1;  
     for (i=2;i<=n;i++)  
        if (c[i]==0)  
           nr++;  
}   


int main()
{
    f>>n;
    ciur();
    g<<nr<<"\n";
}