import java.util.Stack;

class Solution {
    public int calPoints(String[] operations) {
        Stack<String> stack = new Stack<String>();

        for (int i = 0; i < operations.length; i++) {
            if (operations[i].equals("D")) {
                int peeked = Integer.parseInt(stack.peek());
                stack.push(Integer.toString(peeked * 2));
            }
            else if (operations[i].equals("C")) {
                stack.pop();
            }
            else if (operations[i].equals("+")) {
                String popped = stack.pop();
                int operand1 = Integer.parseInt(popped);
                int operand2 = Integer.parseInt(stack.peek());
                stack.push(popped);
                stack.push(Integer.toString(operand1 + operand2));
            }
            else {
                // an integer
                stack.push(operations[i]);
            }
        }

        int sum = 0;
        while (!stack.isEmpty()) {
            sum += Integer.parseInt(stack.pop());
        }

        return sum;
    }
}