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# (Mono-mcs 6.8.0.105) (judge verdict: Wrong Answer)

using System;

namespace ABC171C
{
    class Program
    {
        static void Main(string[] args)
        {
            ulong n = ulong.Parse(Console.ReadLine());
            ulong[] a = new ulong[12];
            string s = null ;
            int f = 1;
            for(int i = 10; i>=1;i--)
            {
                a[f] = n / (ulong)Math.Pow(26,i) ;
                n = n % (ulong)(Math.Pow(26, i));
                f++;

            }

            for(int i = 0;i<f;i++)
            {
                
                if ((a[i] != 0 && n != 0) ||(s != null))
                {
                    if(a[i] == 1)
                    {
                        s += "a";
                    }
                    if (a[i] == 2)
                    {
                        s += "b";
                    }
                    if (a[i] == 3)
                    {
                        s += "c";
                    }
                    if (a[i] == 4)
                    {
                        s += "d";
                    }
                    if (a[i] == 5)
                    {
                        s += "e";
                    }
                    if (a[i] == 6)
                    {
                        s += "f";
                    }
                    if (a[i] == 7)
                    {
                        s += "g";
                    }
                    if (a[i] == 8)
                    {
                        s += "h";
                    }
                    if (a[i] == 9)
                    {
                        s += "i";
                    }
                    if (a[i] == 10)
                    {
                        s += "j";
                    }
                    if (a[i] == 11)
                    {
                        s += "k";
                    }
                    if (a[i] == 12)
                    {
                        s += "l";
                    }
                    if (a[i] == 13)
                    {
                        s += "m";
                    }
                    if (a[i] == 14)
                    {
                        s += "n";
                    }
                    if (a[i] == 15)
                    {
                        s += "o";
                    }
                    if (a[i] == 16)
                    {
                        s += "p";
                    }
                    if (a[i] == 17)
                    {
                        s += "q";
                    }
                    if (a[i] == 18)
                    {
                        s += "r";
                    }
                    if (a[i] == 19)
                    {
                        s += "s";
                    }
                    if (a[i] == 20)
                    {
                        s += "t";
                    }
                    if (a[i] == 21)
                    {
                        s += "u";
                    }
                    if (a[i] == 22)
                    {
                        s += "v";
                    }
                    if (a[i] == 23)
                    {
                        s += "w";
                    }
                    if (a[i] == 24)
                    {
                        s += "x";
                    }
                    if (a[i] == 25)
                    {
                        s += "y";
                    }
                    if (a[i] == 26)
                    {
                        s += "z";
                    }


                }
                if (a[i] != 0 && n == 0)
                {
                    if (a[i] - 1 == 1)
                    {
                        s += "a";
                    }
                    if (a[i] - 1 == 2)
                    {
                        s += "b";
                    }
                    if (a[i] - 1 == 3)
                    {
                        s += "c";
                    }
                    if (a[i] - 1 == 4)
                    {
                        s += "d";
                    }
                    if (a[i] - 1 == 5)
                    {
                        s += "e";
                    }
                    if (a[i] - 1 == 6)
                    {
                        s += "f";
                    }
                    if (a[i] - 1 == 7)
                    {
                        s += "g";
                    }
                    if (a[i] - 1 == 8)
                    {
                        s += "h";
                    }
                    if (a[i] - 1 == 9)
                    {
                        s += "i";
                    }
                    if (a[i] - 1 == 10)
                    {
                        s += "j";
                    }
                    if (a[i] - 1 == 11)
                    {
                        s += "k";
                    }
                    if (a[i] - 1 == 12)
                    {
                        s += "l";
                    }
                    if (a[i] - 1 == 13)
                    {
                        s += "m";
                    }
                    if (a[i] - 1 == 14)
                    {
                        s += "n";
                    }
                    if (a[i] - 1 == 15)
                    {
                        s += "o";
                    }
                    if (a[i] - 1 == 16)
                    {
                        s += "p";
                    }
                    if (a[i] - 1 == 17)
                    {
                        s += "q";
                    }
                    if (a[i] - 1 == 18)
                    {
                        s += "r";
                    }
                    if (a[i] - 1 == 19)
                    {
                        s += "s";
                    }
                    if (a[i] - 1 == 20)
                    {
                        s += "t";
                    }
                    if (a[i] - 1 == 21)
                    {
                        s += "u";
                    }
                    if (a[i] - 1 == 22)
                    {
                        s += "v";
                    }
                    if (a[i] - 1 == 23)
                    {
                        s += "w";
                    }
                    if (a[i] - 1 == 24)
                    {
                        s += "x";
                    }
                    if (a[i] - 1 == 25)
                    {
                        s += "y";
                    }
                    if (a[i] - 1 == 0)
                    {
                        s += "z";
                    }
                }
             }

            
            if (n == 1)
            {
                s += "a";
            }
            if (n == 2)
            {
                s += "b";
            }
            if (n == 3)
            {
                s += "c";
            }
            if (n == 4)
            {
                s += "d";
            }
            if (n == 5)
            {
                s += "e";
            }
            if (n == 6)
            {
                s += "f";
            }
            if (n == 7)
            {
                s += "g";
            }
            if (n == 8)
            {
                s += "h";
            }
            if (n == 9)
            {
                s += "i";
            }
            if (n == 10)
            {
                s += "j";
            }
            if (n == 11)
            {
                s += "k";
            }
            if (n == 12)
            {
                s += "l";
            }
            if (n == 13)
            {
                s += "m";
            }
            if (n == 14)
            {
                s += "n";
            }
            if (n == 15)
            {
                s += "o";
            }
            if (n == 16)
            {
                s += "p";
            }
            if (n == 17)
            {
                s += "q";
            }
            if (n == 18)
            {
                s += "r";
            }
            if (n == 19)
            {
                s += "s";
            }
            if (n == 20)
            {
                s += "t";
            }
            if (n == 21)
            {
                s += "u";
            }
            if (n == 22)
            {
                s += "v";
            }
            if (n == 23)
            {
                s += "w";
            }
            if (n == 24)
            {
                s += "x";
            }
            if (n == 25)
            {
                s += "y";
            }
            //if (n == 0 )
            //{
            //    s += "z";
            //}

            Console.WriteLine(s);
        }
    }
}