codreforces C. Replace To Make Regular Bracket Sequence（栈）

C. Replace To Make Regular Bracket Sequence

time limit per test

1 second

memory limit per test

256 megabytes

input

standard input

output

standard output

You are given string s consists of opening and closing brackets of four kinds <>, {}, [], (). 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 < by the bracket {, but you can't replace it by ) or >.

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 s1 and s2 be a RBS then the strings <s1>s2, {s1}s2, [s1]s2,(s1)s2 are also RBS.

For example the string "[[(){}]<>]" is RBS, but the strings "[)()" and "][()()" are not.

Determine the least number of replaces to make the string s RBS.

Input

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 106.

Output

If it's impossible to get RBS from s print Impossible.

Otherwise print the least number of replaces needed to get RBS from s.

Examples

input

[<}){}

output

2

input

{()}[]

output

0

input

]]

output

Impossible

#include<cstdio>#include<cstring>#include<stack>using namespace std;int main(){    char s[1000000+10];    while(~scanf("%s",s))    {    int falg = 0;    int l = strlen(s);    if(l % 2 == 1)       printf("Impossible\n");    else    {    stack<char> st;    for(int i = 0 ; i < l ; i++)        {        if(st.empty())           st.push(s[i]);           else           {              if(s[i] == '(' || s[i] == '<' || s[i] == '{' || s[i] == '[')               st.push(s[i]);               else if(s[i] == ')' && st.top() == '(')               st.pop();           else if(s[i] == ']' && st.top() == '[')               st.pop();           else if(s[i] == '>' && st.top() == '<')                st.pop();           else if(s[i] == '}' && st.top() == '{')                st.pop();           else           {             if(st.top() == '(' || st.top() == '<' ||st.top() == '{' || st.top() == '[')             {             falg++;                st.pop(); }                else                   st.push(s[i]);           }  }       }     if(st.empty())        printf("%d\n",falg);    else       printf("Impossible\n");}}return 0;}