Parsing a postfix expression in C#, my naive approach

namespace Postfix
{
    class Parser
    {
        static Dictionary<string, Func<int, int, int>> operators;
        static Regex parserEngine = new Regex(@"\G(\s+(?<op>[-+*/])|\s*(?<value>-?[0-9]+))", RegexOptions.ExplicitCapture);

        static Parser()
        {
            operators = new Dictionary<string, Func<int, int, int>>();
            operators["+"] = (a, b) => a + b;
            operators["-"] = (a, b) => a - b;
            operators["*"] = (a, b) => a * b;
            operators["/"] = (a, b) => a / b;
        }

        static int parseExp(string s)
        {
            Stack<int> stack = new Stack<int>();

            foreach(Match match in parserEngine.Matches(s))
            {
                if(match.Success)
                {
                    foreach(KeyValuePair<string, string> m in match.Groups)
                    {
                        if(m.Key == "op")
                        {
                            if(stack.Count < 2)
                                throw new Exception("Invalid expression: out of stack.");
                            int b = stack.Pop();
                            int a = stack.Pop();
                            stack.Push(operators[m.Value](a, b));
                        }
                        else if(m.Key == "value")
                            stack.Push(int.Parse(m.Value));
                    }
                }
            }

            if(stack.Count != 1)
                throw new Exception("Invalid expression: not exactly one result on stack.");

            return stack.Pop();
        }

        static void Main()
        {
            string exp = "23 5 - 12 *";
            Console.WriteLine("expression '{0}' result is '{1}'", exp, Parser.parseExp(exp));
        }
    }
}