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Counter-Strike: Source is a remake of Counter-Strike, and retains its team-based objective-oriented first-person shooter style gameplay. The aim of playing a map is to accomplish a map's objective: defusing the bomb, rescuing all hostages, or killing the entire opposing team. The ultimate goal of the game is to win more rounds than the opposing team. 

Here is the link to the game :
http://www.mediafire.com/download/21z1jqrbp9qsthr/Counter%20strike%20Source%202011.iso