Consider quadratic Diophantine equations of the form:

~~~
x^2 – Dy^2 = 1
~~~

For example, when `D=13`, the minimal solution in `x` is `649^2 – 13×180^2 = 1`.

It can be assumed that there are no solutions in positive integers when D is square.

By finding minimal solutions in `x` for `D = {2, 3, 5, 6, 7}`, we obtain the following:

~~~
3^2 – 2×2^2 = 1
2^2 – 3×1^2 = 1
9^2 – 5×4^2 = 1
5^2 – 6×2^2 = 1
8^2 – 7×3^2 = 1
~~~

Hence, by considering minimal solutions in `x` for `D <= 7`, the largest `x` is obtained when `D=5`.

Find the value of `D <= 1000` in minimal solutions of `x` for which the largest value of `x` is obtained.