import java.util.Scanner;

// 注意类名必须为 Main, 不要有任何 package xxx 信息
public class Main {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);

        scanner.useDelimiter("\n");
        while (scanner.hasNextInt()) {
            int i = scanner.nextInt();
            int res = 0;
            for (int j = 0; j <= i; j++) {
                String ping = j * j + "";
                String original = j + "";
                if (ping.endsWith(original)) {
                    res++;
                }
            }
            System.out.println(res);
        }
    }
}