import java.util.Scanner;
import java.util.Stack;
import java.util.EmptyStackException;

// bracket matching based on Algorithm on p201 Goodrich & Tamassia

public class BrackMatch
{
   public static void main(String args[]) {
       System.out.println("Enter input tokens separated by spaces");
       System.out.println("Terminate input with ^D");
       Stack s = new Stack();
       Scanner i = new Scanner(System.in);
       try {
          while (i.hasNext()) {
            String b = i.next();
            if (openBrac(b)) s.push(b);
            if (closeBrac(b)) {
                if (s.empty()) throw new RuntimeException("Unmatched " + b);
                String c = (String) s.pop();
                if (!matchBrac(c, b)) 
                   throw new RuntimeException("Mismatched " + c + b);
            }
          }
          if (s.empty()) System.out.println("Brackets are OK");
          else throw new RuntimeException("Unmatched " + s.pop());
       } catch (RuntimeException e) {
           System.out.println("Error: " + e);
       }
   }
   
//------------------------ helper methods are below -------------------

   public static boolean openBrac(String x) {
       if (x.equals("(") || x.equals("{") || x.equals("["))
           return true;
       return false;
   }
   public static boolean closeBrac(String x) {
       if (x.equals(")") || x.equals("}") || x.equals("]"))
           return true;
       return false;
   }
   public static boolean matchBrac(String x, String y) {
       if (x.equals("(") && y.equals(")")) return true;
       if (x.equals("{") && y.equals("}")) return true;       
       if (x.equals("[") && y.equals("]")) return true;
       return false;
   }
}