#include <fstream>
#include <iostream>
#include <string>
using namespace std;


string findresult(std::string& input) {
    string result = "";
    int maxDepth = -1;
    int currentDepth = 0;
    bool flag = false;
    for (char c : input) {
        if (c == '(' || c == '{' || c == '[') {
            currentDepth++;
            if (currentDepth > maxDepth) {
                flag = false;
                maxDepth = currentDepth;
                result = "";
            }
        }
        else if (c == ')' || c == '}' || c == ']') {
            if (currentDepth == maxDepth) {
                flag = true;
            }
            currentDepth = 0;

        }
        else if (currentDepth == maxDepth and !flag) {
            result += c;
        }
        cout << result << endl;
    }

    return result;
}
int main()
{
    ifstream input("input.txt");
    ofstream output("output.txt");
    string read = "";
    string cur = "";
    while (!input.eof()) {
        getline(input, cur);
        read += cur;
        cur = "";
    }
    string result = findresult(read);
    output << result;
}