Top-level const doesn't influence a function s

Question

From the C++ Primer 5th Edition, it says:

int f(int){ /* can write to parameter */}
int f(const int){ /* cannot write to parameter */}

The two functions are indistinguishable. But as you know, the two functions really differ in how they can update their parameters.

Can someone explains to me?

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EDIT
I think I didn't interpret my question well. What I really care is why C++ doesn't allow these two functions simultaneously as different function since they are really different as to "whether parameter can be written or not". Intuitively, it should be!

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EDIT
The nature of pass by value is actually pass by copying argument values to parameter values. Even for references and pointers where thee copied values are addresses. From the caller's viewpoint, whether const or non-const is passed to the function does not influence values (and of course types of) copied to parameters.
The distinction between top-level const and low-level const matters when copying objects. More specifically, top-level const(not the case of low-level const) is ignored when copying objects since copying won't influence the copied object. It is immaterial whether the object copied to or copied from is const or not.
So for the caller, differentiating them is not necessary. Likely, from the function viewpoint, the top-level const parameters doesn't influence the interface and/or the functionality of function. The two function actually accomplish the same thing. Why bother implementing two copies?

Answer 1

A function is useful only from the caller's perspective.

Since there is no difference to the caller, there is no difference, for these two functions.