Buggy python submission (verdict: Time Limit Exceeded):
s = list(input().strip())
N = len(s)
a = ""
for i in range(N):
    if s[i]!="x":
        a += s[i]
if a==a[::-1]:
    flag = 1
else:
    flag = 0
if flag==1:
    y = list(s[:])
    cur = 0
    cnt = 0
    while True:
        if y[cur]==y[len(y)-1-cur]:
            cur += 1
        else:
            cnt += 1
            if y[cur]=="x":
                y = y[:len(y)-cur]+["x"]+y[len(y)-cur:]
            else:
                y = y[:cur]+["x"]+y[cur:]
        if y==y[::-1]:break
if flag==0:
    print(-1)
else:
    print(cnt)

Fixed submission:
import math
s = input().strip()
A = []
B = [0 for _ in range(len(s)+1)]
y = ""
for i in range(len(s)):
    if s[i]!="x":
        y += s[i]
        A.append(i)
        B[i+1] = B[i]
    else:
        B[i+1] = B[i]+1
flag=0
cnt = 0
for i in range(len(y)//2):
    if y[i]!=y[-(i+1)]:
        flag = 1
        cnt = -1
        break
if flag==0 and len(y)>0:
    if B[A[0]]!=B[-1]-B[A[-1]]:
        cnt += abs(B[A[0]]-(B[-1]-B[A[-1]]))
    for i in range(1,math.ceil(len(A)/2)):
        if B[A[i]]-B[A[i-1]] != B[A[-i]]-B[A[-(i+1)]]:
            cnt += abs(B[A[i]]-B[A[i-1]]-(B[A[-i]]-B[A[-(i+1)]]))
print(cnt)

Buggy python submission (verdict: Runtime Error):
s = list(input().strip())
N = len(s)
a = ""
for i in range(N):
    if s[i]!="x":
        a += s[i]
if a==a[::-1]:
    flag = 1
else:
    flag = 0
if flag==1:
    n = len(a)
    C = [0 for _ in range(2*n+1)]
    for i in range(1,2*n+1,2):
        C[i] = a[i//2]
    cur = 0
    ind = 0
    for i in range(N):
        if s[i]=="x":
            C[cur]="x"
            cur += 2
        else:
            if 2*ind+1>cur:
                cur += 2
            ind += 1
    cnt = 0
    for i in range(0,n,2):
        if C[i]!=C[2*n-i]:
            cnt += 1
if flag==0:
    print(-1)
else:
    print(cnt)

Fixed submission:
import math
s = input().strip()
A = []
B = [0 for _ in range(len(s)+1)]
y = ""
for i in range(len(s)):
    if s[i]!="x":
        y += s[i]
        A.append(i)
        B[i+1] = B[i]
    else:
        B[i+1] = B[i]+1
flag=0
cnt = 0
for i in range(len(y)//2):
    if y[i]!=y[-(i+1)]:
        flag = 1
        cnt = -1
        break
if flag==0 and len(y)>0:
    if B[A[0]]!=B[-1]-B[A[-1]]:
        cnt += abs(B[A[0]]-(B[-1]-B[A[-1]]))
    for i in range(1,math.ceil(len(A)/2)):
        if B[A[i]]-B[A[i-1]] != B[A[-i]]-B[A[-(i+1)]]:
            cnt += abs(B[A[i]]-B[A[i-1]]-(B[A[-i]]-B[A[-(i+1)]]))
print(cnt)

Buggy python submission (verdict: Runtime Error):
import math
s = input().strip()
A = []
B = [0 for _ in range(len(s)+1)]
y = ""
for i in range(len(s)):
    if s[i]!="x":
        y += s[i]
        A.append(i)
        B[i+1] = B[i]
    else:
        B[i+1] = B[i]+1
flag=0
cnt = 0
for i in range(len(y)//2):
    if y[i]!=y[-(i+1)]:
        flag=1
        cnt = -1
        break
if flag==0:
    if B[A[0]]!=B[-1]-B[A[-1]]:
        cnt += abs(B[A[0]]-(B[-1]-B[A[-1]]))
    for i in range(1,math.ceil(len(A)/2)):
        if B[A[i]]-B[A[i-1]] != B[A[-i]]-B[A[-(i+1)]]:
            cnt += abs(B[A[i]]-B[A[i-1]]-(B[A[-i]]-B[A[-(i+1)]]))
print(cnt)

Fixed submission:
import math
s = input().strip()
A = []
B = [0 for _ in range(len(s)+1)]
y = ""
for i in range(len(s)):
    if s[i]!="x":
        y += s[i]
        A.append(i)
        B[i+1] = B[i]
    else:
        B[i+1] = B[i]+1
flag=0
cnt = 0
for i in range(len(y)//2):
    if y[i]!=y[-(i+1)]:
        flag = 1
        cnt = -1
        break
if flag==0 and len(y)>0:
    if B[A[0]]!=B[-1]-B[A[-1]]:
        cnt += abs(B[A[0]]-(B[-1]-B[A[-1]]))
    for i in range(1,math.ceil(len(A)/2)):
        if B[A[i]]-B[A[i-1]] != B[A[-i]]-B[A[-(i+1)]]:
            cnt += abs(B[A[i]]-B[A[i-1]]-(B[A[-i]]-B[A[-(i+1)]]))
print(cnt)