/* 
02.    
ciurul lui eratostene 
03. 
*/
#include <fstream> 
#include <iostream> 
using namespace std; 

char v[2000001];
int main(){ 
    

    
int n ,r, i , j; 
    
ifstream fin("ciur.in"); fin>>n;fin.close(); 
    

    
for(i=0;i<=n;i++) 
        
v[i]=1; 
    
r=1,i=2;for(j=2;j*i<=n;j++)  v[i*j] = 0; 
    
for(i=3;i<=n;i+=2) 
        
if(v[i]==1) 
            
for(j=2,r++;j*i<=n;j++) 
                
v[i*j] = 0; 
    
ofstream fout("ciur.out"); fout<<r; fout.close(); 
    
return 0; 
}