1110

import java.io.*;

public class Main {
	public static void main(String[] args) throws IOException {
		BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
		int input = Integer.parseInt(br.readLine());
		int a = input/10;
		int b = input%10;
		int cnt = 0;
		int result;
		while (true){
			cnt++;
			result = (b*10) + (a+b)%10;
			a = result/10;
			b = result%10;
			//System.out.println("Step" + cnt + ": " + result + " a: " + a + ", b: " + b);
			if(result == input){
				break;
			}
		}

		System.out.println(cnt);
	}
}

다른 사람꺼 퍼옴

import java.util.Scanner;
 
public class Main {
 
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        sc.close();
         
        int number = n;
        int count = 0;
         
        do {
            number = number % 10 * 10 + (number / 10 + number % 10) % 10;
            count++;
        } while (n != number);
         
        System.out.println(count);
    }
}