Buggy python submission (verdict: Time Limit Exceeded):

s = input()

a = ''
for i in range(len(s)):
    if s[i]!='x':
        a+=s[i]

b = ''
for i in range(len(a)):
    b+=a[-1-i]

if a!=b:
    print(-1)
else:
    ss = ''
    for i in range(len(s)):
        ss += s[-1-i]
    i = 0
    j=0
    ans = 0
    while True:
        if i>=len(s):
            ans += len(ss)-j
            break
        elif j>=len(ss):
            ans += len(s)-i
            break
        if s[i]!=ss[j]:
            if s[i]=='x':
                i+=1
            else:
                j+=1
            ans += 1
        else:
            i+=1
            j+=1
    print(ans//2)



Fixed submission:
s = input()

a = ''
for i in range(len(s)):
    if s[i]!='x':
        a+=s[i]

b = ''
for i in range(len(a)):
    b+=a[-1-i]

if a!=b:
    print(-1)
else:
    ss = ''
    for i in range(len(s)):
        ss += s[-1-i]
    i = 0
    j=0
    ans = 0
    while True:
        if i>=len(s):
            ans += len(ss)-j
            break
        elif j>=len(ss):
            ans += len(s)-i
            break
        if s[i]!=ss[j]:
            if s[i]=='x':
                i+=1
            else:
                j+=1
            ans += 1
        else:
            i+=1
            j+=1
    print(ans//2)

Buggy python submission (verdict: Time Limit Exceeded):
s = input()

a = ''
ss = ''
b = ''
for i in range(len(s)):
    ss += s[-1-i]
    if s[i]!='x':
        a+=s[i]
        b = s[i]+b

if a!=b:
    print(-1)
else:
    i = 0
    ans = 0
    while s!=ss:
        if i>=len(s):
            ans += len(ss)-i
            break
        elif i>= len(ss):
            ans += len(s)-i
            break
        if s[i]!=ss[i]:
            if s[i]=='x':
                ss = ss[:i]+'x'+ss[i:]
            else:
                s = s[:i]+'x'+s[i:]
            ans += 1
        i+=1
    print(ans//2)



Fixed submission:
s = input()

a = ''
for i in range(len(s)):
    if s[i]!='x':
        a+=s[i]

b = ''
for i in range(len(a)):
    b+=a[-1-i]

if a!=b:
    print(-1)
else:
    ss = ''
    for i in range(len(s)):
        ss += s[-1-i]
    i = 0
    j=0
    ans = 0
    while True:
        if i>=len(s):
            ans += len(ss)-j
            break
        elif j>=len(ss):
            ans += len(s)-i
            break
        if s[i]!=ss[j]:
            if s[i]=='x':
                i+=1
            else:
                j+=1
            ans += 1
        else:
            i+=1
            j+=1
    print(ans//2)

Buggy python submission (verdict: Time Limit Exceeded):
s = input()

a = ''
for i in range(len(s)):
    if s[i]!='x':
        a+=s[i]

b = ''
for i in range(len(a)):
    b+=a[-1-i]

if a!=b:
    print(-1)
else:
    ss = ''
    for i in range(len(s)):
        ss += s[-1-i]
    i = 0
    ans = 0
    while s!=ss:
        if i>=len(s):
            ans += len(ss)-i
            break
        elif i>= len(ss):
            ans += len(s)-i
            break
        if s[i]!=ss[i]:
            if s[i]=='x':
                ss = ss[:i]+'x'+ss[i:]
            else:
                s = s[:i]+'x'+s[i:]
            ans += 1
        i+=1
    print(ans//2)



Fixed submission:
s = input()

a = ''
for i in range(len(s)):
    if s[i]!='x':
        a+=s[i]

b = ''
for i in range(len(a)):
    b+=a[-1-i]

if a!=b:
    print(-1)
else:
    ss = ''
    for i in range(len(s)):
        ss += s[-1-i]
    i = 0
    j=0
    ans = 0
    while True:
        if i>=len(s):
            ans += len(ss)-j
            break
        elif j>=len(ss):
            ans += len(s)-i
            break
        if s[i]!=ss[j]:
            if s[i]=='x':
                i+=1
            else:
                j+=1
            ans += 1
        else:
            i+=1
            j+=1
    print(ans//2)

Buggy python submission (verdict: Time Limit Exceeded):
s = input()

a = ''
for i in range(len(s)):
    if s[i]!='x':
        a+=s[i]

b = ''
for i in range(len(a)):
    b+=a[-1-i]

if a!=b:
    print(-1)
else:
    ss = ''
    for i in range(len(s)):
        ss += s[-1-i]
    i = 0
    ans = 0
    while s!=ss:
        if i>=len(s):
            ans += len(ss)-i
            break
        elif i>= len(ss):
            ans += len(s)-i
            break
        if s[i]!=ss[i]:
            if s[i]=='x':
                ss = ss[:i]+'x'+ss[i:]
            else:
                s = s[:i]+'x'+s[i:]
            ans += 1
        i+=1
    print(ans//2)



Fixed submission:
s = input()

a = ''
for i in range(len(s)):
    if s[i]!='x':
        a+=s[i]

b = ''
for i in range(len(a)):
    b+=a[-1-i]

if a!=b:
    print(-1)
else:
    ss = ''
    for i in range(len(s)):
        ss += s[-1-i]
    i = 0
    j=0
    ans = 0
    while True:
        if i>=len(s):
            ans += len(ss)-j
            break
        elif j>=len(ss):
            ans += len(s)-i
            break
        if s[i]!=ss[j]:
            if s[i]=='x':
                i+=1
            else:
                j+=1
            ans += 1
        else:
            i+=1
            j+=1
    print(ans//2)