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

            }


            Console.WriteLine(s);
            
      
        }
    }
}