C++: how to differentiate fill constructor and range constructor in C++11?

I suspect the prototypes of fill constructor and range constructor of std::vector (and many other STL types) given in this webpage are not right, so I implement a NaiveVector to mimic these two prototypes.

My code is:

#include <iostream>
#include <vector>
using namespace std;

template <typename T>
struct NaiveVector {
  vector<T> v;
  NaiveVector(size_t num, const T &val) : v(num, val) {
    cout << "(int num, T val)" << endl;
  }

  template <typename InputIterator>
  NaiveVector(InputIterator first, InputIterator last) : v(first, last) {
    cout << "(InputIterator first, InputIterator last)" << endl;
  }

  size_t size() const { return v.size(); }
};

int main() {
  NaiveVector<int> myVec1(5,1);
  cout << "size = " << myVec1.size() << endl;
  for (auto n : myVec1.v) { cout << n << " "; }
  cout << endl;

  cout << "-----" << endl;

  vector<int> vec({1,2,3,4,5});
  NaiveVector<int> myVec2(vec.begin(), vec.end());
  cout << "size = " << myVec2.size() << endl;
  for (auto n : myVec2.v) { cout << n << " "; }
  cout << endl;
}

And the output is:

$ g++ overload.cc -o overload -std=c++11
$ ./overload
(InputIterator first, InputIterator last)
size = 5
1 1 1 1 1
-----
(InputIterator first, InputIterator last)
size = 5
1 2 3 4 5

As I suspected from the beginning, the compiler cannot differentiate the two constructors properly. Then my question is: how does std::vector's fill constructor and range constructor differentiate from each other?

Rephrase: how to implement the two constructors of this NaiveVector?

This question seems to be a duplicate of this question but the answer is not satisfying. Additionally, C++11 itself doesn't provide a is_iterator<>.. (MSVC has lots of hacks).