Delete multiple lines from text file using c#

Question

I have a text file containing 100 lines. I want to delete first 20 lines from that file I have a following code

IS anyone tell me how to do that? this code only deleting 1 line. I want to delete first 20 lines

string line = null;
int line_number = 0;
int line_to_delete = 12;

using (StreamReader reader = new StreamReader("C:\\input")) {
    using (StreamWriter writer = new StreamWriter("C:\\output")) {
        while ((line = reader.ReadLine()) != null) {
            line_number++;

            if (line_number == line_to_delete)
                continue;

            writer.WriteLine(line);
        }
    }
}

Answer 1

How about using some Linq and static methods? If performance is not crucial(the code will read all lines into memory):

File.WriteAllLines("outputfile",
    File.ReadLines("inputfile").Skip(20));