#include<fstream> 
using namespace std;

ifstream fin("ciur.in"); 
ofstream fout("ciur.out"); 
char a[2000005]; 
long i,j,n,nr; 
int main() 
{ 
    
nr=0; 
    
fin>>n; 
    
for (i=2;i<=n;i++) 
a[i]=1; 
    
for (i=2;i<=n;i++) 
if (a[i]==1) 
{ 
nr++; 
for (j=2*i;j<=n;j+=i) 
                
a[j]=0; 
        
} 
    
fout<<nr; 
 return 0; 
}