#include <vector>

#include <string>

#include <list>

#include <map>

#include <set>

#include <deque>

#include <stack>

#include <bitset>

#include <algorithm>

#include <functional>

#include <numeric>

#include <utility>

#include <sstream>

#include <iostream>

#include <iomanip>

#include <cstdio>

#include <cmath>

#include <cstdlib>

#include <ctime>

#include <cstring>

#include <climits>

#include <queue>

using namespace std;

class BracketExpressions

{

public:

    string src,dst;

    const string bracket="()[]{}";

    bool check(string& str){

        stack<char> st;

        for(int i =  ; i < str.length(); ++ i){

            if(st.empty()) st.push(str[i]);

            else{

                char ch = st.top();

                if((str[i]==']'&& ch=='[')||(str[i] == '}' && ch=='{') || (str[i]==')'&& ch=='(')) st.top();

                else st.push(str[i]);

            }

        }

        cout<<st.size()<<endl;

        return st.empty()?true:false;

    }

    bool dfs(int cur){

        if(cur==src.length()) return check(dst);

        if(src[cur]=='X'){

            bool flag = false;

            for(int i =  ; i < bracket.length();++i){

                dst[cur]=bracket[i];

                flag|=dfs(cur+);

            }

            return flag;

        }else return dfs(cur+);

    }

    string ifPossible(string expression)

    {

        src=dst=expression;

        return dfs()?"possible":"impossible";

    }

};

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