题解 | #自守数#--遍历，字符串截取

import java.util.*;

public class Main {
    public static void main(String[] args) {
        Scanner in = new Scanner(System.in);
        int num = in.nextInt();
        int count = 0;
        // 判断是否是自守数
        for (int i = 0; i <= num; i++) {
            if (i <= 1) {
                count++;
            } else {
                if (isSelfNum(i)) {
                    count++;
                }
            }
        }
        System.out.println(count);
    }

    private static boolean isSelfNum(int in) {
        int tem = in * in;
        int len1 = String.valueOf(in).length();
        int len2 = String.valueOf(tem).length();
        int tail = Integer.parseInt(String.valueOf(tem).substring(len2 - len1, len2));
        if (tail == in) {
            return true;
        }
        return false;
    }
}