Problem:
Score : 300 points

Problem Statement

1000000000000001 dogs suddenly appeared under the roof of Roger's house, all of which he decided to keep. The dogs had been numbered 1 through 1000000000000001, but he gave them new names, as follows:

the dogs numbered 1,2,\cdots,26 were respectively given the names a, b, ..., z;

the dogs numbered 27,28,29,\cdots,701,702 were respectively given the names aa, ab, ac, ..., zy, zz;

the dogs numbered 703,704,705,\cdots,18277,18278 were respectively given the names aaa, aab, aac, ..., zzy, zzz;

the dogs numbered 18279,18280,18281,\cdots,475253,475254 were respectively given the names aaaa, aaab, aaac, ..., zzzy, zzzz;

the dogs numbered 475255,475256,\cdots were respectively given the names aaaaa, aaaab, ...;

and so on.

To sum it up, the dogs numbered 1, 2, \cdots were respectively given the following names:

a, b, ..., z, aa, ab, ..., az, ba, bb, ..., bz, ..., za, zb, ..., zz, aaa, aab, ..., aaz, aba, abb, ..., abz, ..., zzz, aaaa, ...

Now, Roger asks you:

"What is the name for the dog numbered N?"

Constraints

N is an integer.

1 \leq N \leq 1000000000000001

Input

Input is given from Standard Input in the following format:

N

Output

Print the answer to Roger's question as a string consisting of lowercase English letters.

Sample Input 1

2

Sample Output 1

b

Sample Input 2

27

Sample Output 2

aa

Sample Input 3

123456789

Sample Output 3

jjddja

Solution in C# (.NET Core 3.1.201) (judge verdict: Wrong Answer)

using System;
using System.Collections.Generic;
using System.Linq;
public class Hello
{
    public static void Main()
    {
        //アルファベットテーブルを作成する
        var alpha = new string[26] { "a", "b", "c", "d", "e",
                                     "f", "g", "h", "i", "j", "k",
                                     "l", "m", "n", "o", "p", "q",
                                     "r", "s", "t", "u", "v", "w", 
                                     "X", "y", "Z" };
        var N = long.Parse(Console.ReadLine());
        var e = 1L;
        var cnt = 1;
		//while (26 <= N)
		//=> 最初このような書き方をしていたが、
		//この書き方だとN=701のようなときNが負の値になってしまい、実行時エラーとなる。
        while (e * 27 <= N)
        {
            N = N- (long)Math.Pow(26, cnt);
			//26の階乗の数より小さいかチェックするための変数を設ける
            e *=26;
            cnt++;
        }
        N--;
        var ans = "";
		//最後尾の文字列から順に回答を組み立てていく
        for(int num=cnt-1;0<=num;num--)
        {
            ans=ans +alpha[N%26];
            N /= 26;
        }
        //順番が逆順なので反転して直す
        Console.WriteLine(String.Join("", ans.Reverse()));
    }
}