Implementing the Template Method pattern in C#

The template method pattern provides that the abstract base class has a not overridable method: this method implements the common algorithm and should not overridden in the subclasses. In Java the template method is declared final within the abstract base class, in C# the sealed keyword has a similar meaning, but a not overridden method can not be declared sealed.

public abstract class Base
{
    protected abstract AlgorithmStep1();

    protected abstract AlgorithmStep2();

    public sealed void TemplateMethod()   // sealed: compile error
    {
        AlgorithmStep1();
        AlgorithmStep2();
    }
}

How can I solve this problem? Why can not prevent a method can be overridden by subclasses (in C#)?