import java.util.NoSuchElementException;

interface Stack<E> {

    // Elementi na stekot se objekti od proizvolen tip.

    // Metodi za pristap:

    public boolean isEmpty ();
        // Vrakja true ako i samo ako stekot e prazen.

    public E peek ();
        // Go vrakja elementot na vrvot od stekot.

    // Metodi za transformacija:

    public void clear ();
        // Go prazni stekot.

    public void push (E x);
        // Go dodava x na vrvot na stekot.

    public E pop ();
        // Go otstranuva i vrakja elementot shto e na vrvot na stekot.
}
lass ArrayStack<E> implements Stack<E> {

    // Stekot e pretstaven na sledniot nacin:
    //depth e dlabochinata na stekot, a
    // elems[0...depth-1] se negovite elementi.
    private E[] elems;
    private int depth;

    @SuppressWarnings("unchecked")
    public ArrayStack (int maxDepth) {
        // Konstrukcija na nov, prazen stek.
        elems = (E[]) new Object[maxDepth];
        depth = 0;
    }


    public boolean isEmpty () {
        // Vrakja true ako i samo ako stekot e prazen.
        return (depth == 0);
    }


    public E peek () {
        // Go vrakja elementot na vrvot od stekot.
        if (depth == 0)
            throw new NoSuchElementException();
        return elems[depth-1];
    }


    public void clear () {
        // Go prazni stekot.
        for (int i = 0; i < depth; i++)  elems[i] = null;
        depth = 0;
    }


    public void push (E x) {
        // Go dodava x na vrvot na stekot.
        elems[depth++] = x;
    }


    public E pop () {
        // Go otstranuva i vrakja elementot shto e na vrvot na stekot.
        if (depth == 0)
            throw new NoSuchElementException();
        E topmost = elems[--depth];
        elems[depth] = null;
        return topmost;
    }
}
public class Zagradi {
    public static boolean daliKorektni (String phrase) {
        // Test whether phrase is well-bracketed.
        ArrayStack<Character> bracketStack = new ArrayStack<Character>(100);
        for (int i = 0; i < phrase.length(); i++) {
            char cur = phrase.charAt(i);
            if (cur == '(' || cur == '[' || cur == '{')
                bracketStack.push(cur);
            else if (cur == ')' || cur == ']' || cur == '}') {
                if (bracketStack.isEmpty()) return false;
                char left = bracketStack.pop();
                if (! daliSoodvetni(left, cur)) return false;
            }
        }
        return (bracketStack.isEmpty());
    }

    public static boolean daliSoodvetni (char left, char right) {
        // Test whether left and right are matching brackets
        // (assuming that left is a left bracket and right is a right bracket).
        switch (left) {
            case '(':
                return (right == ')');
            case '[':
                return (right == ']');
            case '{':
                return (right == '}');
        }
        return false;
    }

    public static void main (String[] args) {
         //String phrase = "s x (s – a) x (s – b) x (s – c)";
         String phrase = "s x (s – a) x s – b) x (s – c)";
         System.out.println(phrase + " ima "
                    + (daliKorektni(phrase) ? "korektni" : "nekorektni")
                    + " zagradi.");
    }
}