import java.io.*;
import java.util.Scanner;

public class Main {

    public static void main(String[] args) throws FileNotFoundException{
        final int nmx = 2000005;
        int n, suma = 0;
        boolean viz[] = new boolean[nmx];
        
        Scanner reader = new Scanner(new FileInputStream("ciur.in"));
        n = reader.nextInt();
        reader.close();
        
        for(int i = 2; i <= n; ++i)
            if(viz[i] == false){
                ++ suma;
                for(int j = i + i; j <= n; j += i)
                    viz[j] = true;
            }
        
        PrintWriter writer = new PrintWriter("ciur.out");
        writer.write(suma + "\n");
        writer.close();
        
    }
    
}