Buggy python submission (verdict: Runtime Error):
n=int(input())
al=[chr(ord('a') + i) for i in range(26)]
sakai=[]
k=0
for i in range(10):
  k+=26**(i+1)
  sakai.append(k)

if n<=26:
  n-=1
  u=1
elif n>sakai[9]:
  n-=sakai[9]+1
  u=11
for i in range(9):
  if (sakai[i]<n<=sakai[i+1]):
    n-=sakai[i]+1
    u=i+2

def base(n):
  ans=[]
  while(n>26):
    r=n%26
    n=(n-r)//26
    ans.append(r)
  ans.append(n)
  return ans


p=base(n)

if u-len(p)>0:
  ans_3='a'
  if u-len(p)>1:
    for j in range(u-len(p)-1):
      ans_3+='a'
    
for i in range(len(p)):
  if i==0:
    ans_2=al[p[len(p)-i-1]]
  else:
    ans_2=ans_2+al[p[len(p)-i-1]]
if u-len(p)>0:
  print(ans_3+ans_2)
else:
  print(ans_2)
               

Fixed submission:
n=int(input())
al=[chr(ord('a') + i) for i in range(26)]
sakai=[]
k=0
for i in range(10):
  k+=26**(i+1)
  sakai.append(k)

if n<=26:
  n-=1
  u=1
elif n>sakai[9]:
  n-=sakai[9]+1
  u=11
for i in range(9):
  if (sakai[i]<n<=sakai[i+1]):
    n-=sakai[i]+1
    u=i+2

def base(n):
  ans=[]
  while(n>=26):
    r=n%26
    n=(n-r)//26
    ans.append(r)
  ans.append(n)
  return ans


p=base(n)

if u-len(p)>0:
  ans_3='a'
  if u-len(p)>1:
    for j in range(u-len(p)-1):
      ans_3+='a'
    
for i in range(len(p)):
  if i==0:
    ans_2=al[p[len(p)-i-1]]
  else:
    ans_2=ans_2+al[p[len(p)-i-1]]
if u-len(p)>0:
  print(ans_3+ans_2)
else:
  print(ans_2)

Buggy python submission (verdict: Runtime Error):
n=int(input())
al=[chr(ord('a') + i) for i in range(26)]
sakai=[]
k=0
for i in range(10):
  k+=26**(i+1)
  sakai.append(k)

if n<=26:
  n-=1
  u=1
elif n>sakai[9]:
  n-=sakai[9]+1
  u=11
for i in range(9):
  if (sakai[i]<n<=sakai[i+1]):
    n-=sakai[i]+1
    u=i+2

def base(n):
  ans=[]
  while(n>26):
    r=n%26
    n=(n-r)//26
    ans.append(r)
  ans.append(n)
  return ans


p=base(n)



if u-len(p)>0:
  ans_3='a'
  if u-len(p)>1:
    for j in range(u-len(p)-1):
      ans_3+='a'
    
for i in range(len(p)):
  if i==0:
    ans_2=al[p[len(p)-i-1]]
  elif i==len(p)-1:
    ans_2=ans_2+al[p[len(p)-i-1]]
  else:
    ans_2=ans_2+al[p[len(p)-i-1]]
if u-len(p)>0:
  print(ans_3+ans_2)
else:
  print(ans_2)
               
    

Fixed submission:
n=int(input())
al=[chr(ord('a') + i) for i in range(26)]
sakai=[]
k=0
for i in range(10):
  k+=26**(i+1)
  sakai.append(k)

if n<=26:
  n-=1
  u=1
elif n>sakai[9]:
  n-=sakai[9]+1
  u=11
for i in range(9):
  if (sakai[i]<n<=sakai[i+1]):
    n-=sakai[i]+1
    u=i+2

def base(n):
  ans=[]
  while(n>=26):
    r=n%26
    n=(n-r)//26
    ans.append(r)
  ans.append(n)
  return ans


p=base(n)

if u-len(p)>0:
  ans_3='a'
  if u-len(p)>1:
    for j in range(u-len(p)-1):
      ans_3+='a'
    
for i in range(len(p)):
  if i==0:
    ans_2=al[p[len(p)-i-1]]
  else:
    ans_2=ans_2+al[p[len(p)-i-1]]
if u-len(p)>0:
  print(ans_3+ans_2)
else:
  print(ans_2)

Buggy python submission (verdict: Runtime Error):
n=int(input())
al=[chr(ord('a') + i) for i in range(26)]
sakai=[]
k=0
for i in range(10):
  k+=26**(i+1)
  sakai.append(k)


for i in range(10):
  if (sakai[i]<n<=sakai[i+1]):
    n-=sakai[i]
    u=i+2
  elif (n>sakai[9]):
    n-=sakai[9]
    u=12

def base(n):
  ans=[]
  while(n>26):
    r=n%26
    n=(n-r)//26
    ans.append(r)
  ans.append(n)
  return ans

p=base(n-1)
if u-len(p)>0:
  ans_3='a'
  if u-len(p)>1:
    for j in range(u-len(p)-1):
      ans_3+='a'
    
for i in range(len(p)):
  if i==0:
    ans_2=al[p[len(p)-i-1]]
  else:
    ans_2=ans_2+al[p[len(p)-i-1]]
if u-len(p)>0:
  print(ans_3+ans_2)
else:
  print(ans_2)
               
    

Fixed submission:
n=int(input())
al=[chr(ord('a') + i) for i in range(26)]
sakai=[]
k=0
for i in range(10):
  k+=26**(i+1)
  sakai.append(k)

if n<=26:
  n-=1
  u=1
elif n>sakai[9]:
  n-=sakai[9]+1
  u=11
for i in range(9):
  if (sakai[i]<n<=sakai[i+1]):
    n-=sakai[i]+1
    u=i+2

def base(n):
  ans=[]
  while(n>=26):
    r=n%26
    n=(n-r)//26
    ans.append(r)
  ans.append(n)
  return ans


p=base(n)

if u-len(p)>0:
  ans_3='a'
  if u-len(p)>1:
    for j in range(u-len(p)-1):
      ans_3+='a'
    
for i in range(len(p)):
  if i==0:
    ans_2=al[p[len(p)-i-1]]
  else:
    ans_2=ans_2+al[p[len(p)-i-1]]
if u-len(p)>0:
  print(ans_3+ans_2)
else:
  print(ans_2)