Buggy python submission (verdict: Runtime Error):
#!/usr/bin/env python
# -*- coding: utf-8 -*-

import sys


def input():
    return sys.stdin.readline()

def Base_10_to_n(i10, n, ans_list:list):
    # 各桁を0-indexにするために1減らす
    i10 -= 1
    if(int(i10/n)):
        ans_list.append(Base_10_to_n(int(i10/n), n, ans_list))
        return str(i10%n)
    return str(i10%n)


def resolve():
    n = int(input().rstrip())
    n_list = []
    ans_list = []

    n_list.append(Base_10_to_n(n, 26, n_list))

    for n26 in n_list:
        string = ord("a") + n26
        ans_list.append(chr(string))

    ans_string = ""
    for st in ans_list:
        ans_string += st
    print(ans_string.rstrip())

if __name__ == "__main__":
    resolve()



Fixed submission:
#!/usr/bin/env python
# -*- coding: utf-8 -*-

import sys


def input():
    return sys.stdin.readline()

def Base_10_to_n(i10, n, ans_list:list):
    i10 -= 1
    if(int(i10/n)):
        ans_list.append(Base_10_to_n(int(i10/n), n, ans_list))
        return str(i10%n)
    return str(i10%n)


def resolve():
    n = int(input().rstrip())
    n_list = []

    ans_list = []

    n_list.append(Base_10_to_n(n, 26, n_list))
    n26_list =[]
    for n26 in n_list:
        n26_list.append(int(n26))

    for n26 in n26_list:
        string = ord("a") + n26
        ans_list.append(chr(string))

    ans_string = ""
    for st in ans_list:
        ans_string += st
    print(ans_string.rstrip())

if __name__ == "__main__":
    resolve()

Buggy python submission (verdict: Runtime Error):
#!/usr/bin/env python
# -*- coding: utf-8 -*-

import sys


def input():
    return sys.stdin.readline()

def Base_10_to_n(i10, n, ans_list:list):
    if(int(i10/n)):
        ans_list.append(Base_10_to_n(int(i10/n), n, ans_list))
        return str(i10%n)
    return str(i10%n)


def resolve():
    n = int(input().rstrip())
    n_list = []

    ans_list = []

    n_list.append(Base_10_to_n(n, 26, n_list))
    cnt = 0

    #print(n_list)
    for i in range(len(n_list)):
        #print(ans_list)
        if n_list[i] == "0":
            cnt = 1
            while n_list[i - cnt] == "1":
                #print(ans_list,cnt, i-cnt)
                ans_list.pop(i-cnt)
                ans_list.append("z")
                #print(ans_list)
                if i-cnt == 0:
                    break
                cnt += 1
            #print(i, cnt)
            if n_list[i-cnt] != "1":
                #print(ans_list)
                ord_s = ord(ans_list.pop(i-cnt-1)) -1
                #print(ans_list)
                ans_list.append(chr(ord_s))
                ans_list.append("z")


        else:
            string = ord('a') + int(n_list[i]) -1
            ans_list.append(chr(string))

    ans_string = ""
    for st in ans_list:
        ans_string += st
    print(ans_string.rstrip())

if __name__ == "__main__":
    resolve()



Fixed submission:
#!/usr/bin/env python
# -*- coding: utf-8 -*-

import sys


def input():
    return sys.stdin.readline()

def Base_10_to_n(i10, n, ans_list:list):
    i10 -= 1
    if(int(i10/n)):
        ans_list.append(Base_10_to_n(int(i10/n), n, ans_list))
        return str(i10%n)
    return str(i10%n)


def resolve():
    n = int(input().rstrip())
    n_list = []

    ans_list = []

    n_list.append(Base_10_to_n(n, 26, n_list))
    n26_list =[]
    for n26 in n_list:
        n26_list.append(int(n26))

    for n26 in n26_list:
        string = ord("a") + n26
        ans_list.append(chr(string))

    ans_string = ""
    for st in ans_list:
        ans_string += st
    print(ans_string.rstrip())

if __name__ == "__main__":
    resolve()