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.Linq;
class c
{
    static void Main()
    {
        long n = long.Parse(Console.ReadLine());
        var k = new long[11];
        k[0] = 26;
        for (int i = 1; i < 11; i++)
        {
            k[i] = k[i - 1] + (long)Math.Pow(26, i + 1);
        }
        int L = 0;
        for (int i = 0; i < 11; i++)
        {
            if (k[i] < n) L = i + 1;
        }
        if (L >= 1) n = n - k[L - 1];
        n--;
        var ans = "";
        var num = new int[L + 1];
        for (int i = L; i >= 1; i--)
        {
            while (n - (long)Math.Pow(26, i) >= 0 && num[i] <= 25)
            {
                n -= (long)Math.Pow(26, i);
                num[i]++;
            }
        }
        num[0] = (char)(n );
        for (int i = 0; i <= L; i++)
        {
            ans += (char)(num[i] + 'a');
        }
        Console.WriteLine(string.Join("", ans.Reverse()));
    }
}