You are given string *s* consists of opening and closing brackets of four kinds &lt;&gt;, {}, [], (). There are two types of brackets: opening and closing. You can replace any bracket by another of the same type. For example, you can replace &lt; by the bracket {, but you can't replace it by ) or &gt;.

The following definition of a regular bracket sequence is well-known, so you can be familiar with it.

Let's define a regular bracket sequence (RBS). Empty string is RBS. Let *s*<sub class="lower-index">1</sub> and *s*<sub class="lower-index">2</sub> be a RBS then the strings &lt;*s*<sub class="lower-index">1</sub>&gt;*s*<sub class="lower-index">2</sub>, {*s*<sub class="lower-index">1</sub>}*s*<sub class="lower-index">2</sub>, [*s*<sub class="lower-index">1</sub>]*s*<sub class="lower-index">2</sub>, (*s*<sub class="lower-index">1</sub>)*s*<sub class="lower-index">2</sub> are also RBS.

For example the string "[[(){}]&lt;&gt;]" is RBS, but the strings "[)()" and "][()()" are not.

Determine the least number of replaces to make the string *s* RBS.
The only line contains a non empty string *s*, consisting of only opening and closing brackets of four kinds. The length of *s* does not exceed 10<sup class="upper-index">6</sup>.
none
[<}){}
2
{()}[]
0
]]
Impossible
>
Impossible
{}
0
{}
0
{]
1
{]
1
{]
1
[]{[]({)([
Impossible
(([{>}{[{[)]]>>]
7
((<>)[]<]><]
3
[[([[(>]>)))[<)>
6
({)[}<)](}
5
(}{)[<][)(]}
6
>}({>]{[}<{<{{)[]]{)]>]]]<(][{)<<<{<<)>)()[>{<]]{}<>}}}}(>}<})(][>{((<{<)]}>)))][>[}[])<]){]]][<[)([
Impossible
<<[<{{<([({<<[)<>(]]){})>[](])[)))[[}>]<)>[[>{>>>[<]}<>>)[>]<{)<[><(<]][>(>]>][(<][{]}(()<[()[>><<])<]})]<]}{)
45
[<<{{((}[}<<)<)>})(][{>}})((>)<[)[>}[})[)>()[()[((}<<(>)<>](<>(}[>})[[[{)<}<<(}{>>}[<([[])<><)]<{>}[>>>{({>)}]})>)
42
(<[([(<({>(}{]>[(})])}])()<<}{]{[>]>(>>[(>>}[){(}<[{(()]{{<(<{][[{<><{<{)<>>]}}}{)(}{})}[<))>>}((({>){({}{{]}]>>}})>))
43
{(]}<([]<]{>]<{<({{{<>))}[({(}{)[}({>]}}<<)}<]))(<>(>{>{{{)<}({<]<>{)(>[)>{({}<([<[[)]><>{]}}(>]{}<)[})]}]]}]}>}
40
<(([)]<[}>{)>][[(<()({{{>>((]<}<{{<>}><<[)}[[)([[)[)}<]<{(<>){([)><{[([[][({])})<][(}]}>>[){)[({>){(}[}})>}>]>)]}))})>}]
45
)(
Impossible
[[[[[[[[
Impossible
line = input()
memory = ''
mass = []
left = right = 0
for el in line:
    mass.append(el)
c = 0

if line[0] == ']' or line[0] == '}' or line[0] == ')' or line[0] == '>':
    print('impossible')
    quit()

for g in line:
    if g == '[':
        if ']' in mass[mass.index('['):]:
            mass.remove('[')
            mass.remove(']')
    if g == '{':
        if '}' in mass[mass.index('{'):]:
            mass.remove('}')
            mass.remove('{')
    if g == '<':
        if '>' in mass[mass.index('{'):]:
            mass.remove('>')
            mass.remove('<')
    if g == '(':
        if ')' in mass[mass.index('('):]:
            mass.remove(')')
            mass.remove('(')

if len(mass) % 2 != 0:
    print('impossible')
    quit()



for q in mass:
    if q == '[' or q == '<' or q == '(' or q == '{':
        left += 1
    if q == ']' or q == '>' or q == ')' or q == '}':
        right += 1

if not left == right:
    print('impossible')
    quit()

for i in mass:
    if len(mass) > 0:
        if i == '[':
            if mass[-1] == '}' or mass[-1] == '>' or mass[-1] == ')':
                mass.pop(0)
                mass.pop(-1)
                c += 1
        if i == '{':
            if mass[-1] == ']' or mass[-1] == '>' or mass[-1] == ')':
                mass.pop(0)
                mass.pop(-1)
                c += 1
        if i == '<':
            if mass[-1] == '}' or mass[-1] == ']' or mass[-1] == ')':
                mass.pop(0)
                mass.pop(-1)
                c += 1
        if i == '(':
            if mass[-1] == '}' or mass[-1] == '>' or mass[-1] == ']':
                mass.pop(0)
                mass.pop(-1)
                c += 1
if mass != []:
    for i in mass:
        if i == '[':
            if mass[-1] == '}' or mass[-1] == '>' or mass[-1] == ')':
                mass.pop(0)
                mass.pop(-1)
                c += 1
        if i == '{':
            if mass[-1] == ']' or mass[-1] == '>' or mass[-1] == ')':
                mass.pop(0)
                mass.pop(-1)
                c += 1
        if i == '<':
            if mass[-1] == '}' or mass[-1] == ']' or mass[-1] == ')':
                mass.pop(0)
                mass.pop(-1)
                c += 1
        if i == '(':
            if mass[-1] == '}' or mass[-1] == '>' or mass[-1] == ']':
                mass.pop(0)
                mass.pop(-1)
                c += 1

print(c)