using System;
using System.Text.RegularExpressions;
public class Example
{
public static void Main()
{
string pattern = @"((\d*[1-9]\d*)[0](\d*[1-9]\d*)|(\d*[2-9]\d*)[1](\d*[2-9]\d*)|(\d*[3-9]\d*)[2](\d*[3-9]\d*)|(\d*[4-9]\d*)[3](\d*[4-9]\d*)|(\d*[5-9]\d*)[4](\d*[5-9]\d*)|(\d*[6-9]\d*)[5](\d*[6-9]\d*)|(\d*[7-9]\d*)[6](\d*[7-9]\d*)|(\d*[8-9]\d*)[7](\d*[8-9]\d*)|(\d*[9]\d*)[8](\d*[9]\d*))|((\d*[0-8]\d*)[9](\d*[0-8]\d*)|(\d*[0-7]\d*)[8](\d*[0-7]\d*)|(\d*[0-6]\d*)[7](\d*[0-6]\d*)|(\d*[0-5]\d*)[6](\d*[0-5]\d*)|(\d*[0-4]\d*)[5](\d*[0-4]\d*)|(\d*[0-3]\d*)[4](\d*[0-3]\d*)|(\d*[0-2]\d*)[3](\d*[0-2]\d*)|(\d*[0-1]\d*)[2](\d*[0-1]\d*)|(\d*[0]\d*)[1](\d*[0]\d*))";
string input = @"123
234567
0123456789
87654
321
985
346
320
12342
7655338
9876789
2000000001";
foreach (Match m in Regex.Matches(input, pattern))
{
Console.WriteLine("'{0}' found at index {1}.", m.Value, m.Index);
}
}
}
Please keep in mind that these code samples are automatically generated and are not guaranteed to work. If you find any syntax errors, feel free to submit a bug report. For a full regex reference for C#, please visit: https://msdn.microsoft.com/en-us/library/system.text.regularexpressions.regex(v=vs.110).aspx