# include <fstream>
 #define N 2000001  
 using namespace std;
 char c[N];  
 long long n;  
 void ciur()  
 {  
   int d=2;  
   while (d*d<=n)  
   {  
         
      if (!c[d])  
         for (int i=d*d; i<=n; i+=d)  
             c[i]=1;++d;  
   }  
   long long num=0;  
   for (int i=2; i<=n; ++i) 
   if (!c[i]) num++;  
   
   ofstream g("ciur.out");
   g<<num;
   g.close();
     
 }  
 void citire()  
 {  
   ifstream f("ciur.in");  
   f>>n;  
   f.close();
 }  
 int main()  
 {  
   citire();  
   ciur();  
   return 0;  
}