Solution Review: Big (O) of Nested Loop with Subtraction

namespace Chapter_1
{
    class Challenge2
    {
        static void Main(string[] args)
        {
            int n = 10;   
            int sum = 0;
            float pie = 3.14f;
            for (int i = n; i >= 1; i -= 3) // O(n/3)
            {
                Console.WriteLine(pie); // O(n/3)
                for (int j = n; j >= 0; j--)  // O((n/3)*(n+1))
                {
                    sum += 1;   // O((n/3)*(n+1))
                }
            }
            Console.WriteLine(sum);
            return;
        }
    }
}