def eco(s):
    if not s.isalpha() or len(s)%2 != 1:
        return '-1-'
    else:
        midpos = len(s) // 2
        par1 = s[0:midpos].upper()
        par2 = s[midpos+1:].upper()
        if par1 == par2:
            return s[midpos]
        else:
            return '-2-'