题解 | 无限长正整数排列字符串

using System;
public class Program {
    public static void Main() {
        int X=int.Parse(Console.ReadLine());
        if(X<=9)
        {
            Console.WriteLine(X);
        }else if(X>=10&&X<=189)
        {
            if(X%2==0)
            {
                Console.WriteLine((X-10)/20+1);   
            }else{
                Console.WriteLine((X-11)/2%10); 
            }
        }else
        {   
            if(X%3==1){
                Console.WriteLine((X-190)/300+1); 
            }else if(X%3==2){
                Console.WriteLine(((X-191)/30)%10);
            }else{
                Console.WriteLine((X-192)/3%10);
            }
            
        }

    }
}