Buggy python submission (verdict: Runtime Error):
import math
s = list(str(input()))
lis = ""
li = ""
num = 0
cou = [0 for i in range(26)]
for i in range(len(s)):
  if s[i] != "x":
    lis += s[i]
    li = s[i] + li
  else:
    num += 1
if lis != li:
  print(-1)
  exit()
point = lis[len(lis)//2]
ss = ["1"]
tt = ["1"]
nu = 0
while s[nu] != point:
  ss.append(s[nu])
  nu += 1
nu = 0
while s[-1-nu] != point:
  tt.append(s[-1-nu])
  nu += 1
ans = 0
for i in range(max(len(ss),len(tt))):
  try:
    if ss[i] != tt[i]:
      ans += 1
  except:
    ans += 1
print(ans)

Fixed submission:
import math
s = str(input())
cou = 0
co = 0
ans = 0
while cou + co +2 <= len(s):
  if s[cou] == "x":
    if s[-1-co] == "x":
      cou += 1
      co += 1
    else:
      cou += 1
      ans += 1
  else:
    if s[-1-co] == "x":
      co += 1
      ans += 1
    else:
      if s[cou] == s[-1-co]:
        cou += 1
        co += 1
      else:
        print(-1)
        exit()
print(ans)

Buggy python submission (verdict: Runtime Error):
import math
s = list(str(input()))
lis = ""
li = ""
num = 0
cou = [0 for i in range(26)]
for i in range(len(s)):
  if s[i] != "x":
    lis += s[i]
    li = s[i] + li
  else:
    num += 1
if lis != li:
  print(-1)
  exit()
point = lis[len(lis)//2]
ss = ["1"]
tt = ["1"]
nu = 0
while s[nu] != point:
  ss.append(s[nu])
  nu += 1
nu = 0
while s[-1-nu] != point:
  tt.append(s[-1-nu])
  nu += 1
ans = 0
for i in range(max(len(ss),len(tt))):
  try:
    if ss[i] != tt[i]:
      ans += 1
  except:
    ans += 1
print(ans,ss,tt)

Fixed submission:
import math
s = str(input())
cou = 0
co = 0
ans = 0
while cou + co +2 <= len(s):
  if s[cou] == "x":
    if s[-1-co] == "x":
      cou += 1
      co += 1
    else:
      cou += 1
      ans += 1
  else:
    if s[-1-co] == "x":
      co += 1
      ans += 1
    else:
      if s[cou] == s[-1-co]:
        cou += 1
        co += 1
      else:
        print(-1)
        exit()
print(ans)

Buggy python submission (verdict: Runtime Error):
import math
s = list(str(input()))
lis = ""
li = ""
num = 0
cou = [0 for i in range(26)]
for i in range(len(s)):
  if s[i] != "x":
    lis += s[i]
    li = s[i] + li
  else:
    num += 1
if lis != li:
  print(-1)
  exit()
point = lis[len(lis)//2]
ss = []
tt = []
nu = 0
while s[nu] != point:
  ss.append(s[nu])
  nu += 1
nu = 0
while s[-1-nu] != point:
  tt.append(s[-1-nu])
  nu += 1
ans = 0
for i in range(len(ss)):
  if ss[i] != tt[i]:
    ans += 1
print(ans)

Fixed submission:
import math
s = str(input())
cou = 0
co = 0
ans = 0
while cou + co +2 <= len(s):
  if s[cou] == "x":
    if s[-1-co] == "x":
      cou += 1
      co += 1
    else:
      cou += 1
      ans += 1
  else:
    if s[-1-co] == "x":
      co += 1
      ans += 1
    else:
      if s[cou] == s[-1-co]:
        cou += 1
        co += 1
      else:
        print(-1)
        exit()
print(ans)

Buggy python submission (verdict: Runtime Error):
import math
s = list(str(input()))
lis = ""
li = ""
num = 0
cou = [0 for i in range(26)]
for i in range(len(s)):
  if s[i] != "x":
    lis += s[i]
    li = s[i] + li
  else:
    num += 1
if lis != li:
  print(-1)
  exit()
point = lis[len(lis)//2]
ss = []
tt = []
nu = 0
while s[nu] != point:
  ss.append(s[nu])
  nu += 1
nu = 0
while s[-1-nu] != point:
  tt.append(s[-1-nu])
  nu += 1
ans = 0
for i in range(n):
  if ss[i] != tt[i]:
    ans += 1
print(ans)

Fixed submission:
import math
s = str(input())
cou = 0
co = 0
ans = 0
while cou + co +2 <= len(s):
  if s[cou] == "x":
    if s[-1-co] == "x":
      cou += 1
      co += 1
    else:
      cou += 1
      ans += 1
  else:
    if s[-1-co] == "x":
      co += 1
      ans += 1
    else:
      if s[cou] == s[-1-co]:
        cou += 1
        co += 1
      else:
        print(-1)
        exit()
print(ans)