public int evalRPN(String[] tokens) {
		if (tokens.length == 0) {
			return 0;
		}
		Stack<Integer> stack = new Stack<Integer>();
		for (String token : tokens) {
			try {
				int i = Integer.valueOf(token);
				stack.push(i);
			} catch (NumberFormatException e) {
				int a = stack.pop();
				int b = stack.pop();
				if (token.equals("+")) {
					stack.push(a + b);
				} else if (token.equals("-")) {
					stack.push(b - a);
				} else if (token.equals("*")) {
					stack.push(b * a);
				} else if (token.equals("/")) {
					stack.push(b / a);
				}
			}
		}
		return stack.pop();
	}