C#：簡單遞歸累加算法

namespace demo
{
    public class Program
    {
        static void Main(string[] args)
        {
            int res = Sum(100);
        }        
        static int Sum(int n)
        {
            if (n <= 1)
                return n;
            return n+Sum(n - 1);
        }
    }
}