Error bounds with approximated M value

[elemental_d]

How do you approximate the value 'M' for the error bound formula for the Trapezoid Rule of a function that the derivative cannot be found?

Error Bound Formula: http://archives.math.utk.edu/visual.calculus/4/approx.2/index.html

I'm trying to figure out the value of n to get erf(1.00) approximated within the error of 0.001?

Error Function: http://en.wikipedia.org/wiki/Error_function

How do i get M(in the error bound formula) when it is not possible to get the second derivative of the error function?

 

[DeadWolfe]

But it IS possible to get the second derivative of erf.