题解 | 大水题 c#

using System;
using System.Collections.Generic;
using System.Linq;
public class Program {
    public static void Main() {
        Console.WriteLine(BigWaterExercise(Console.ReadLine()));
    }
    public static int BigWaterExercise(string num) {
        if (num.Length == 1) {
            return int.Parse(num);
        } else {
            int sum = 0;
            foreach (char c in num) {
                sum += int.Parse(c.ToString());
            }
            return BigWaterExercise(sum.ToString());
        }


    }
}