public boolean isValid(String s) {

        Stack<Character> leftSymbols = new Stack<>();

        for (int i = 0; i < s.length(); i++) {
            char c = s.charAt(i);
            if (c == '(' || c == '{' || c == '[') {
                leftSymbols.push(c);
            } else {
                if (leftSymbols.isEmpty()) return false;

                char ch = leftSymbols.pop();
                if ((ch == '(' && c != ')') ||
                        (ch == '[' && c != ']') ||
                        (ch == '{' && c != '}')) {
                    return false;
                }
            }
        }
        return leftSymbols.isEmpty();
    }

class MyQueue {

    Stack<Integer> in;
    Stack<Integer> out;

    public MyQueue() {
        in = new Stack<>();
        out = new Stack<>();
    }

    public void push(int x) {
        in.push(x);
    }

    public int pop() {
        if (out.isEmpty()) {
            while (!in.isEmpty()) {
            out.add(in.pop());
            }
        }
        return out.pop();
    }

    public int peek() {
        if (out.isEmpty()) {
            while (!in.isEmpty()) {
            out.add(in.pop());
            }
        }


        return out.peek();
    }

    public boolean empty() {
        return in.isEmpty() && out.isEmpty();
    }
}