Limit exchange space _ 20200215155746. After thinking about it, Yi Chi decided to create a creation, of course, to make some preparations in advance, for example, to exchange some professional knowledge or something. ...... "Yitang, is the exchange of array knowledge expensive?" After thinking about it, Yi Chi asked Yi Tang. Fortunately, the knowledge of the array is graded, and the price of the low-level ones is cheaper. The answer...