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: Accepted)

using System;
using System.Collections.Generic;

namespace abc171
{
    class Program
    {
        static long max = 1000000000000001L;
        static void Main()
        {
            var n = long.Parse(Console.ReadLine()) - 1;
            var endList = CreateEndList();
            var len = 0;
            var offsetN = 0L;
            for (var i = 1; i < endList.Count; ++i)
            {
                if (n < endList[i])
                {
                    len = i;
                    offsetN = n - endList[i - 1];
                    break;
                }
            }
            var name = new List<char>();
            for (var l = 0; l < len; ++l)
            {
                name.Add((char)((offsetN % 26) + 'a'));
                offsetN /= 26;
            }
            name.Reverse();
            Console.WriteLine(string.Concat(name));
        }
        static List<long> CreateEndList()
        {
            var endList = new List<long>();
            endList.Add(0L);
            var last = 0L;
            var count = 1;
            while(last < max)
            {
                var sameLenCount = 26L;
                for (var i = 1; i < count; ++i)
                {
                    sameLenCount *= 26L;
                }
                sameLenCount += last;
                endList.Add(sameLenCount);
                last = sameLenCount;
                ++count;
            }
            return endList; 
        }
    }
}