问文件拆分中缺少行

EN

using System.IO;
using System;
class MainClass {
  public static void Main(string[] args){

    string line; 
    int linesNumber = 0, linesEach = 0, cont = 0;

    StreamReader r = new StreamReader("in.csv");
    StreamWriter w1 = new StreamWriter("out-1.csv");
    StreamWriter w2 = new StreamWriter("out-2.csv");
    StreamWriter w3 = new StreamWriter("out-3.csv");
    StreamWriter w4 = new StreamWriter("out-4.csv");

    while((line = r.ReadLine()) != null)
      ++linesNumber;

    linesEach = linesNumber / 4;

    r.DiscardBufferedData();
    r.BaseStream.Seek(0, SeekOrigin.Begin);
    r.BaseStream.Position = 0;

    while((line = r.ReadLine()) != null){
      ++cont;
      if(cont == 1){
        //fisrt line must be skipped
        continue;
      }
      if(cont < linesEach){
        Console.WriteLine(line);
        w1.WriteLine(line);
      }
      else if(cont < (linesEach*2)){
        w2.WriteLine(line);
      }
      else if(cont < (linesEach*3)){
        w3.WriteLine(line);
      }
      else{
        w4.WriteLine(line);
      }
    }
  }
}