Four Points on a Semicircle

Geometry Level 3

A semicircle has $AB$ as the endpoints of its diameter, and $AB= 400$ . Points $C$ and $D$ are on the circumference of the semicircle such that $AD = BC = 100$ . What is the length of $DC$ ?

Details and assumptions:

Lengths given are always the straight line distance between two points, unless otherwise indicated.