Help find the error please

I wrote the code, its essence is to place brackets so that the answer is the maximum example input 1 + 2 * 3-2 * 4 output 28 and my code outputs 20 Help solve the error

<pre>ops = ('+-*')
s = input( f'Enter an arithmetic expression with operation signs { list(ops) }: ' )
lis = list( map( lambda x: ') '+x+' (' if x in ops else x, list(s) ) )
s = ''.join(lis)
s = '(' + s + ')'
max_val = float('-inf')
max_str = None
par_count = s.count( '(' ) + s.count( ')' )
for i in range( 2 ** par_count ):
    b = bin(i)[2:].zfill(par_count)
    b_ind = 0
    ss = ''
    for symb in s:
        if symb in '()':
            ss += ( '',symb )[ int( b[b_ind] ) ]
            b_ind += 1
        else:
            ss += symb
    try:
        val = eval( ss )
        if val > max_val:
            max_val = val
            max_str = ss
    except:
        pass
print( f'{ max_str } = { max_val }' )