Buggy python submission (verdict: Runtime Error):
s = list(input())
n = len(s)
x = s.count("x")
a = n-x
if a%2:
    count = 0
    for i in range(n):
        if s[i] != "x":
            count += 1
        if count == a-a//2:
            ind = i
            break
    count = 0
    l = ind-1
    r = ind+1
    c1 = a//2
    while c1 > 0:
        lc = 0
        while l >= 0 and s[l] == "x":
            l += 1
            lc += 1
        rc = 0
        while r < n and s[r] == "x":
            r += 1
            rc += 1
        if s[l] == s[r]:
            count += abs(lc-rc)
            l -= 1
            r += 1
        else:
            print(-1)
            exit()
        c1 -= 1
    count += abs(n-r-(l+1))
    print(count)
else:
    count = 0
    for i in range(n):
        if s[i] != "x":
            count += 1
        if count == a//2:
            l = i
        elif count == a//2+1:
            r = i
            break
    count = 0
    if s[l] != s[r]:
        print(-1)
        exit()
    c1 = a//2-1
    while c1 > 0:
        lc = 0
        while l >= 0 and s[l] == "x":
            l += 1
            lc += 1
        rc = 0
        while r < n and s[r] == "x":
            r += 1
            rc += 1
        if s[l] == s[r]:
            count += abs(lc-rc)
            l -= 1
            r += 1
        else:
            print(-1)
            exit()
        c1 -= 1
    count += abs(n-r-(l+1))
    print(count)

Fixed submission:
s = list(input())
ans = 0
l = 0
r = len(s)-1
while l < r:
    if s[l] != s[r]:
        if s[l] == "x":
            ans += 1
            r += 1
        elif s[r] == "x":
            ans += 1
            l -= 1
        else:
            print(-1)
            exit()
    l += 1
    r -= 1
print(ans)

Buggy python submission (verdict: Runtime Error):
s = list(input())
n = len(s)
x = s.count("x")
a = n-x
if a%2:
    count = 0
    for i in range(n):
        if s[i] != "x":
            count += 1
        if count == a-a//2:
            ind = i
            break
    count = 0
    l = ind-1
    r = ind+1
    c1 = a//2
    while c1 > 0:
        lc = 0
        while l >= 0 and s[l] == "x":
            l += 1
            lc += 1
        rc = 0
        while r < n and s[r] == "x":
            r += 1
            rc += 1
        if s[l] == s[r]:
            count += abs(lc-rc)
            l -= 1
            r += 1
        else:
            print(-1)
            exit()
        c1 -= 1
    count += abs(n-r-(l+1))
    print(count)
else:
    count = 0
    for i in range(n):
        if s[i] != "x":
            count += 1
        if count == a//2:
            l = i
        elif count == a//2+1:
            r = i
            break
    count = 0
    c1 = a//2-1
    while c1 > 0:
        lc = 0
        while l >= 0 and s[l] == "x":
            l += 1
            lc += 1
        rc = 0
        while r < n and s[r] == "x":
            r += 1
            rc += 1
        if s[l] == s[r]:
            count += abs(lc-rc)
            l -= 1
            r += 1
        else:
            print(-1)
            exit()
        c1 -= 1
    count += abs(n-r-(l+1))
    print(count)

Fixed submission:
s = list(input())
ans = 0
l = 0
r = len(s)-1
while l < r:
    if s[l] != s[r]:
        if s[l] == "x":
            ans += 1
            r += 1
        elif s[r] == "x":
            ans += 1
            l -= 1
        else:
            print(-1)
            exit()
    l += 1
    r -= 1
print(ans)