题解 | #自守数#

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 in = new Scanner(System.in);
        int n = in.nextInt();
        int count = 0;
        int mod = 10;
        for (int i = 0; i <= n; i++) {
            if (i>mod) mod*=10;
            if (i*i%mod==i) count++;
        }
        System.out.println(count);
    }
}