# 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;  
}