using System;
using System.Text.RegularExpressions;
public class Test
{
public static void Main()
{
String input = @"start123start123
start123endstart345end
start567endstart789end";
Regex rgx = new Regex(@"(?<=start)\d+(?=end)");
foreach (Match m in rgx.Matches(input))
Console.WriteLine(m.Value);
}
}
dXNpbmcgU3lzdGVtOwp1c2luZyBTeXN0ZW0uVGV4dC5SZWd1bGFyRXhwcmVzc2lvbnM7CiAKcHVibGljIGNsYXNzIFRlc3QKewpwdWJsaWMgc3RhdGljIHZvaWQgTWFpbigpCnsKU3RyaW5nIGlucHV0ID0gQCJzdGFydDEyM3N0YXJ0MTIzCnN0YXJ0MTIzZW5kc3RhcnQzNDVlbmQKc3RhcnQ1NjdlbmRzdGFydDc4OWVuZCI7ClJlZ2V4IHJneCA9IG5ldyBSZWdleChAIig/PD1zdGFydClcZCsoPz1lbmQpIik7CmZvcmVhY2ggKE1hdGNoIG0gaW4gcmd4Lk1hdGNoZXMoaW5wdXQpKQpDb25zb2xlLldyaXRlTGluZShtLlZhbHVlKTsKfQp9