#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;  
 }