C++ ambiguous operator for template overload

I have problem with operator overloading:
I want to write a class with operator like this:

class BigNum
{
    public:
        template<class T>
        bool operator==(const T &input);
        template<class T>
        friend bool operator==(const T &A,BigNum & B);
};

It’s fine to call:

BigNum A;
int a;
A==a;
a==A;

But when calling:

BigNum A,B;
A==B;

It will get the compiler error:

[Error] ambiguous overload for ‘operator==’ (operand types are ‘BigNum’ and ‘BigNum’)
[Note] bool BigNum::operator==(const T&) [with T = BigNum]
[Note] bool operator==(const T&, BigNum&) [with T = BigNum]

And there is same problem if I change

template<class T>
bool operator==(const T &input);

to

bool operator==(const BigNum &input);

But it is OK if the operator overloads are like this(but it can’t doAny type==BigNum):

class BigNum
{
    public:
        bool operator==(const BigNum &input);
        template<class T>
        bool operator==(const T &input);
};

If I want to write the operator overload so that it can do all of these:

• Any type == BigNum
• BigNum == Any type
• BigNum == BigNum

How should I fix it?Thank you.