import java.io.FileInputStream;
import java.io.IOException;
import java.io.PrintStream;
import java.util.Scanner;

public class Ciur {
	public static String IN_FILE = "ciur.in";
	public static String OUT_FILE = "ciur.out";
	
	public static void main(String[] args) throws IOException {
		Scanner scanner = new Scanner(new FileInputStream(IN_FILE));
		
		int n = scanner.nextInt();
		
		scanner.close();
		
		boolean[] sieve = new boolean[n + 1];
		
		for (int i = 0; i <= n; i++) {
			sieve[i] = true;
		}
		
		int count = 0;
		
		for (int i = 2; i <= n; i++) {
			if (!sieve[i]) {
				continue;
			}
			count++;
			for (int j = i + i; j <= n; j += i) {
				sieve[j] = false;
			}
		}
		
		PrintStream printer = new PrintStream(OUT_FILE);
		
		printer.println(count);
		
		printer.close();
	}
}