using System;
using System.Text.RegularExpressions;

public class Test
{
	public static void Main()
	{
		string[] strings = { "/api/ping.json",
                "/api/ping",
                "/api/ping/xxx/sss.json",
                "/api/ping.xml",
                "/api/ping/.json",
                "/api/pingpong",
                "/api/ping_pong",
                "/api/ping-pong"
                };
            string pattern = @"/api/ping(?:(?:/[^/\s]+)*\.\S+|$)";
            foreach (String s in strings) {
                if (Regex.IsMatch(s, pattern)) {
                    Console.WriteLine("Valid: {0}", s);
                } else {
                    Console.WriteLine("Invalid: {0}", s);
                }
            }
	}
}