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

//No.327 アルファベット列
class Program
{
    static string InputPattern = "InputX";

    static List<string> GetInputList()
    {
        var WillReturn = new List<string>();

        if (InputPattern == "Input1") {
            WillReturn.Add("0");
            //A
        }
        else if (InputPattern == "Input2") {
            WillReturn.Add("25");
            //Z
        }
        else if (InputPattern == "Input3") {
            WillReturn.Add("26");
            //AA
        }
        else {
            string wkStr;
            while ((wkStr = Console.ReadLine()) != null) WillReturn.Add(wkStr);
        }
        return WillReturn;
    }

    static void Main()
    {
        List<string> InputList = GetInputList();
        long N = long.Parse(InputList[0]);

        Solve(N);
    }

    static void Solve(long pN)
    {
        long ZentaiBanme = pN + 1; //全体の何番目を求めるか

        //群ごとの項数を求める
        long CurrGunCnt = 26;
        var GunKousuuList = new List<long>();
        while (true) {
            GunKousuuList.Add(CurrGunCnt);
            if (GunKousuuList.Sum() > ZentaiBanme) break;
            CurrGunCnt *= 26;
        }

        long RunSum = 0;
        long GunBanme = ZentaiBanme; //対象群の何番目を求めるか
        long TargetGunLength = 1;
        for (int I = 0; I <= GunKousuuList.Count - 1; I++) {
            RunSum += GunKousuuList[I];
            if (ZentaiBanme <= RunSum) {
                TargetGunLength = I + 1;
                break;
            }
            GunBanme -= GunKousuuList[I];
        }

        long TargetNum = GunBanme - 1;
        var NumList = new List<long>();
        do {
            NumList.Add(TargetNum % 26);
            TargetNum /= 26;
        } while (TargetNum > 0);
        while (NumList.Count < TargetGunLength) NumList.Add(0);
        NumList.Reverse();

        var sb = new System.Text.StringBuilder();
        int UB = NumList.Count - 1;
        for (int I = 0; I <= UB; I++) {
            char wkChar = (char)('A' + (char)NumList[I]);
            sb.Append(wkChar);
        }
        Console.WriteLine(sb.ToString());
    }
}