using System;
using System.Collections.Generic;
using System.Linq;

namespace AtCoder.Question
{
    public class QuestionC
    {
        public static void Main(string[] args)
        {
            var n = ReadHelper.ReadValue<long>();
            var length = 1;
            var sikii = 26L;
            var hiki = 0L;
            while (n > sikii)
            {
                length++;
                var t = 1L;
                for (int i = 0; i < length; i++)
                {
                    t *= 26;
                }
                hiki = sikii;
                sikii += t;
            }
            var result = "";
            n -= (hiki + 1);
            for (int i = 1; i <= length; i++)
            {
                var t = 1L;
                for (int j = 0; j < length - i; j++)
                {
                    t *= 26;
                }
                var c = (char)((int)'a' + ((n / t) % 26));
                result += c.ToString();
            }
            Console.WriteLine(result);
        }

        static class ReadHelper
        {
            internal static T ReadValue<T>()
            {
                return (T)Convert.ChangeType(Console.ReadLine(), typeof(T));
            }
            internal static (T1, T2) ReadValue<T1, T2>()
            {
                var input = Console.ReadLine().Split(' ');
                return ((T1)Convert.ChangeType(input[0], typeof(T1)), (T2)Convert.ChangeType(input[1], typeof(T2)));
            }
            internal static (T1, T2, T3) ReadValue<T1, T2, T3>()
            {
                var input = Console.ReadLine().Split(' ');
                return ((T1)Convert.ChangeType(input[0], typeof(T1)), (T2)Convert.ChangeType(input[1], typeof(T2)), (T3)Convert.ChangeType(input[2], typeof(T3)));
            }
            internal static (T1, T2, T3, T4) ReadValue<T1, T2, T3, T4>()
            {
                var input = Console.ReadLine().Split(' ');
                return ((T1)Convert.ChangeType(input[0], typeof(T1)), (T2)Convert.ChangeType(input[1], typeof(T2)), (T3)Convert.ChangeType(input[2], typeof(T3)), (T4)Convert.ChangeType(input[3], typeof(T4)));
            }
            internal static T[] ReadValues<T>()
            {
                var input = Console.ReadLine().Split(' ');
                return input.Select(x => (T)Convert.ChangeType(x, typeof(T))).ToArray();
            }
        }

        static class MathAlgorithm
        {
            internal static bool IsPrime(long n)
            {
                if (n == 2) return true;
                if (n < 2 || n % 2 == 0) return false;
                var sqrt = Math.Sqrt(n);
                for (int i = 3; i <= sqrt; i += 2) if (n % i == 0) return false;
                return true;
            }
            internal static IEnumerable<long> EnumeratePrimes(long n)
            {
                var i = 2L;
                while (i * i <= n)
                {
                    if (n % i == 0)
                    {
                        n /= i;
                        yield return i;
                    }
                    else
                    {
                        i += i == 2 ? 1 : 2;
                    }
                }
                if (n != 1) yield return n;
            }
        }
    }
}


Measured memory_bytes: 27584