Combinatorics book??

Hello, I am searching for a good book that will deal with counting and combinatorics.....At the moment I am at a low level so I am looking for something intermediate to get on with in the future....I am in a need specificly of something (in English) that will help me for math olympiads and have the style of them...If anyone has any suggestions please do not hessitate to answer...I will be gratefull to any ideas...Thank you for taking this post into consideration.....