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: Runtime Error)

using System;
using System.Collections.Generic;
using System.Linq;
using System.Numerics;
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[27] { "z", "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" };
        BigInteger N = BigInteger.Parse(Console.ReadLine());
        if (N <= 26)
        {
            Console.WriteLine(alpha[(int)N]);
            return;
        }
        BigInteger baisuu26 = 26;
        BigInteger max = 0;
        var e = 2;
        var ans = "";
        while (true)
        {
            baisuu26 = baisuu26 + (BigInteger)Math.Pow(26, e);
            if (N == baisuu26)
            {
                for (var cnt = 0; cnt < e; cnt++)
                {
                    ans += "z";
                }
                break;
            }
            else if (N < baisuu26)
            {
                var sho = N;
                var temp = N;
                for (var num = 1; num < e; num++)
                {
                    sho = sho / 26;
                    //amari = amari % 26;
                    ans = ans.Insert(0,alpha[(int)temp % 26]);
                    temp = sho;
                }
                ans = ans.Insert(0, alpha[(int)sho]);
                break;
            }
            e += 1;
        }
        Console.WriteLine(ans);
    }
}