Problem with Split () on Mono

This is my code:

        string a = Console.ReadLine();

        string[] temp = a.Split(" ");

        List<double> maior = new List<double>();
        maior.Add(double.Parse(temp[0]));
        maior.Add(double.Parse(temp[1]));
        maior.Add(double.Parse(temp[2]));
        maior.Sort();

        Console.WriteLine(maior[2]+ " eh o maior"); 

In my PC I use .NET Core, and it works without error, however when I run into the platform system this error:

Main.cs(10,31): error CS1502: The best overloaded method match for 'string.Split(params char[])' has some invalid arguments
/usr/lib/mono/4.5/mscorlib.dll (Location of the symbol related to previous error)
Main.cs(10,37): error CS1503: Argument '#1' cannot convert 'string' expression to type 'char[]'

Link site with exercise .

Website Mono is in version: 5.4.0