24 с арифм выражением

#https://inf-ege.sdamgia.ru/problem?id=78049
s = open('24_78049.txt').readline()
s = s.replace('6', '!')
s = s.replace('7', '!')
s = s.replace('8', '!')
s = s.replace('9', '!')
s = s.split('!')
answ = 0
for e in s:
    for l in range(len(e)):
        for r in range(l, len(e)):
            S = e[l:r+1]
            if (S[0] != '-') and ('--' not in S) and ('**' not in S) and ('*-' not in S):
                try:
                    eval(S)
                except Exception:
                    pass #ничего не делать
                else:
                    if len(S) > answ:
                        answ = len(S)
print(answ)