prevent checking many conditions in 'if'

could anyone please write an alternate efficient code which prevents checking so many conditions in the if statement

var excludeurl = XMLUtils.GetElementText(instrument.Element("url"));
if (excludeurl != "abc.pdf" && excludeurl != "a.pdf" && excludeurl != "b" && excludeurl != "d" && excludeurl != "e"
&& excludeurl != "f" && excludeurl != "g" && excludeurl != "h" && excludeurl != "i" && excludeurl != "j" && excludeurl != "k" && excludeurl != "l" && excludeurl != "m" && excludeurl != "n" && excludeurl != "o" && excludeurl != "p" && excludeurl != "q" && excludeurl != "r" && excludeurl != "s" && e ...