if n == 1 and k > 0:
        return '9'
    count = sum([1 for i in range(n//2) if s[i] != s[-i-1]])
    if k < count:
        return '-1'
    ex = k-count
    s = list(s)
    for i in range(n//2):
        if s[i] == s[-i-1] != '9' and ex > 1:
            s[i] = s[-i-1] = '9'
            ex -=2
        elif s[i] != s[-i-1]:
            if s[i] == '9' or s[-i-1] == '9':
                s[i] = s[-i-1] = '9'
            else:
                if ex > 0:
                    s[i] = s[-i - 1] = '9'
                    ex -= 1
                else:
                    s[i] = s[-i - 1] = max(s[i], s[-i - 1])
    if ex > 0 and n % 2 == 1:
        s[n//2] = '9'
    return ''.join(s)