C#字符串 如何获取字符串aj4mabcgjabp3cadm2abcjtt中abc之间的字符串.如果其间还有换行，该怎么办

using System;
using System.Collections.Generic;
using System.Text;

namespace ConsoleApplication2
{
class Program
{
static void Main(string[] args)
{
string s = "aj4mabcgjabp3cadm2abcjtt";
int start = s.IndexOf("abc");
int end = s.IndexOf("abc", start + 3);
string result = s.Substring(start + 3, end - start - 3);
Console.WriteLine(result);
}
}
}

//调试了没有问题

string tmpStr = "aj4mabcgjabp3cadm2abcjtt";
string[] result;
string[] strSeparators = new string[] { "abc" };

result = tmpStr.Split(strSeparators, 5,StringSplitOptions.RemoveEmptyEntries);

foreach (string item in result)
{
Console.Write("<{0}>", item);
}
Console.Write("\n\n");

这