declare a vector through decltype

#include "stdafx.h"
#include <iostream>

#include <vector>
#include <map>

template <typename T>
auto Copy(T c)
{
    std::vector<decltype(c.begin()->first)> lc;

   //Copying

    return lc;

}

int main()
{
    std::map<int, int> map;

    Copy(map);


    return 0;
}

In the above code I am trying declare a vector from the datatype of keys of map but I am getting following error -

"The C++ Standard forbids containers of const elements allocator<const T> is ill-formed." 

How can I achieve my motive. Please guide.