24 набрать макс сумму

#https://postimg.cc/Xpdnmg0H
data = open('24.txt').readline()
mx = -10000000000
cur_sm = 0
cur_ch = ''
f = False
for i in range(len(data)):
    if data[i] in '123456789':
        if f:
            cur_ch += data[i]
    if data[i] == '+':
        if f and len(cur_ch) != 0:
            cur_sm += int(cur_ch)
            cur_ch = ''
        else:
            mx = max(mx, cur_sm)
            cur_sm = 0
            f = False
    if data[i] in 'ABCD-*':
        if len(cur_ch) != 0:
            cur_sm += int(cur_ch)
            cur_ch = ''
        mx = max(mx, cur_sm)
        cur_sm = 0
        f = False
        if data[i] == 'D':
            f = True
if len(cur_ch) != 0:
    cur_sm += int(cur_ch)
    cur_ch = ''
mx = max(mx, cur_sm)
print(mx)