public int evalRPN(String[] tokens) {
		Stack<Integer> stack = new Stack<Integer>();
		for (String s : tokens) {
			if (s.equals("+")) {
				int second = stack.pop();
				int first = stack.pop();
				int result = first + second;
				stack.push(result);

			} else if (s.equals("-")) {
				int second = stack.pop();
				int first = stack.pop();
				int result = first - second;
				stack.push(result);

			} else if (s.equals("*")) {
				int second = stack.pop();
				int first = stack.pop();
				int result = first * second;
				stack.push(result);

			} else if (s.equals("/")) {
				int second = stack.pop();
				int first = stack.pop();
				int result = first / second;
				stack.push(result);

			} else {
				int i = Integer.parseInt(s);
				stack.push(i);
			}
		}
		return stack.pop();
	}