Split with multiple delimiter character

Recently I have received an excel file in which one column formatted the AD users in "ID:FirstName,LastName". I need to split the string ID only from the above string.I spent couple of hours to do it generic collection / LinQ based.But finally I end up with the classic way of splitting the string. Here is my workaround.

List list = new List();
List list2 = new List();
string input="MBUPN1:Murugesan,Pandian,MBUPN2:Murugesan,Pandian,MBUPN3:Murugesan,Pandian";
string[] parts1 = input.Split(',');
for (int str = 0; str < parts1.Length; str++)
{
if (parts1[str].Contains(":"))
{
list.Add(parts1[str]);
}
}
foreach (string zz in list)
{
string[] len = zz.Split(':');
list2.Add(len[0].ToString());
}
foreach (string K in list2)
{
 Response.Write(K);
}