Buggy python submission (verdict: Runtime Error):
s = input()
left = 0
right = len(s) - 1
x_left = 0
x_right = 0
if len(s) >= 2:
    while (left <= right):
        if s[left] == s[right]:
            left += 1
            right -= 1
        elif s[left] == "x":
            x_left += 1
            left += 1
        elif s[right] == "x":
            x_right += 1
            right -= 1
        if (right - left == 1) & (s[left] != s[right]):
            if (s[left] != "x") & (s[right] != "x"):
                print(-1)
                exit()
            else:
                print(x_left + x_right + 1)
                exit()
    print(x_left + x_right)
else:
    print(0)

Fixed submission:
s = input()
left = 0
right = len(s) - 1
x_left = 0
x_right = 0
if len(s) >= 2:
    while (left <= right):
        if s[left] == s[right]:
            left += 1
            right -= 1
        elif s[left] == "x":
            x_left += 1
            left += 1
        elif s[right] == "x":
            x_right += 1
            right -= 1
        else:
            print(-1)
            exit()
    print(x_left + x_right)
else:
    print(0)

Buggy python submission (verdict: Runtime Error):
s = input()
left = 0
right = len(s) - 1
x_left = 0
x_right = 0
if len(s) >= 2:
    while (left <= right):
        if s[left] == s[right]:
            left += 1
            right -= 1
        elif s[left] == "x":
            x_left += 1
            left += 1
        elif s[right] == "x":
            x_right += 1
            right -= 1
        if (right - left == 1) & (s[left] != s[right]):
            if (s[left] != "x") & (s[right] != "x"):
                print(-1)
                exit()
    print(x_left + x_right)
else:
    print(0)

Fixed submission:
s = input()
left = 0
right = len(s) - 1
x_left = 0
x_right = 0
if len(s) >= 2:
    while (left <= right):
        if s[left] == s[right]:
            left += 1
            right -= 1
        elif s[left] == "x":
            x_left += 1
            left += 1
        elif s[right] == "x":
            x_right += 1
            right -= 1
        else:
            print(-1)
            exit()
    print(x_left + x_right)
else:
    print(0)

Buggy python submission (verdict: Runtime Error):
s = input()
left = 0
right = len(s) - 1
x_left = 0
x_right = 0
if len(s) > 2:
    while (left <= right):
        if s[left] == s[right]:
            left += 1
            right -= 1
        elif s[left] == "x":
            x_left += 1
            left += 1
        elif s[right] == "x":
            x_right += 1
            right -= 1
        if (right - left == 1) & (s[left] != s[right]):
            if (s[left] != "x") & (s[right] != "x"):
                print(-1)
                exit()
    print(x_left + x_right)
else:
    print(0)           

Fixed submission:
s = input()
left = 0
right = len(s) - 1
x_left = 0
x_right = 0
if len(s) >= 2:
    while (left <= right):
        if s[left] == s[right]:
            left += 1
            right -= 1
        elif s[left] == "x":
            x_left += 1
            left += 1
        elif s[right] == "x":
            x_right += 1
            right -= 1
        else:
            print(-1)
            exit()
    print(x_left + x_right)
else:
    print(0)