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 Java (OpenJDK 1.8.0) (judge verdict: Accepted)

import java.math.BigInteger;
    import java.util.*;
    import java.util.stream.Collectors;

public class Main {
  public static void main(String[] args) {
    Scanner sc = new Scanner(System.in);
    BigInteger n = new BigInteger(sc.next());
    BigInteger c26 = new BigInteger("26");
    BigInteger tmp = BigInteger.ONE;
    BigInteger sum = BigInteger.ONE;
    int digit = 1;
    while (true) {
      tmp = tmp.multiply(c26);
      BigInteger t = sum.add(tmp);
      if (t.compareTo(n) <= 0) {
        digit++;
        sum = t;
      } else {
        break;
      }
    }

    BigInteger remain = n.subtract(sum);
    String s = remain.toString(26);

    Map<Character, String> map = new HashMap<>();
    for (char i = 'a'; i <= 'z'; i++) {
      map.put(BigInteger.valueOf(i - 'a').toString(26).charAt(0), Character.toString(i));
    }
    if (s.length() < digit) {
      String t = "";
      for (int i = 0, len = digit - s.length(); i < len; i++) {
        t += "0";
      }
      s = t + s;
    }
    String result = "";
    for (int i = 0; i < digit; i++) {
      result += map.get(s.charAt(i));
    }
    System.out.println(result);
  }
}