Steps:
1.Create a task
2.Add a variable named %nrange and set it to -1,-2,-3,-4,6,700,800(any number seperated by commas)
3.Add AutoTools Maths Task and set input to %nrange and check Max and Min
4.Add AutoTools Dialog Task and set it to Min: %atmin Max: %atmax
Download the attached file for an example.

Get minimum and maximum values from a list 2017-09-12
Max and Min Finder