If you are still not confident in your ability to both stay sane and repeatedly type std:: over and over, you can explicitly use the specific things you want:
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The goal is just to never ever write "using namespace std;" or similar, because it's like opening the floodgates for your friends - you have no idea about the massive flood of other things that come in.
I usually recommend the std:: method. I recommend always keeping the using declarations as local as possible. For example if I'm using cout and endl in a function quite a lot I might put the using std::cout; statement inside that function. This limits the scope of the using declaration to that function.
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... The rest of the function.