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 static System.Console;
using static System.Math;
public static class Program
{
  public static void Main()
  {
    var n = long.Parse(ReadLine());
    int t;
    long count = 0;
    for (t = 1; ; ++t)
    {
      if (n <= count + (long)Pow(26, t)) break;
      count += (long)Pow(26, t);
    }
    n -= count;
    long temp = n;
    string ans = "";
    for (int i = t - 1; 0 <= i; --i)
    {
      var temp1 = temp;
      var c = 0;
      while(temp1 > 0)
      {
        temp1 -= (long)Pow(26, i);
        c++;
      }
      temp -= (c-1) * (long)Pow(26, i);
      if(i == 0) ans += (char)('a' + c - 1);
      else ans += (char)('a' + c - 1);
    }
    WriteLine(ans);
  }
}