#include<fstream> 
#include <iostream>  
using namespace std; 
char prim[2000001]; 
long n,i,j,nr=0; 
int main() 
 { 
ifstream f("ciur.in"); 
f>>n;
f.close(); 
          
for (i=2;i<=n;i++) 
 prim[i]=1; 
for (i=2;i<=n;i++) 
 if(prim[i]) 
  { 
     nr++; 
     for(j=i+i;j<=n;j=j+i) 
     prim[j]=0; 
                             } 
     ofstream g("ciur.out"); 
     g<<nr; 
     g.close(); 
    return 0; 
}