using System;

public class Test

{

    public static void Main()

    {

        System.Console.WriteLine(getWazeURL("hola mundo de https://holaflow.love asda", "https"));

    }

    public static string getWazeURL(string message, string startSubstring){

        string[]words=message.Split(' ');

        string wazeURL=null;

        foreach(string word in words){

            if(word.StartsWith(startSubstring)){

                wazeURL = word;

                break;

            }

        }

        return wazeURL;

    }

}

​