>for sure i want to knw C++ and JAVA. But i dnt knw the third!
If you want to go the practical route, select a language you're likely to use. Perl and Python are both good options. If you intend to do web programming then PHP would be a good idea, and depending on what systems you want to specialize in, one of the .NET languages could help.
If you want to push your limits as a programmer, select a language that's fundamentally different than C++ and Java, such as one of the LISP variants, Haskell, or assembly.
You will not know only three languages. There is no way. You will end up accidentally having to write a few SQL queries, then some build scripts, editor customizations, web server configurations, XML transformations, ...........
And before you know it, you'll have learned too many languages! Time to bang your head against the wall so that you can go back down to three.