ILL 1984 Problem 39

Let $ABC$ be an isosceles triangle, $AB = AC, \angle A = 20^{\circ}$ . Let $D$ be a point on $AB$ , and $E$ a point on $AC$ such that $\angle ACD = 20^{\circ}$ and $\angle ABE = 30^{\circ}$ . What is the measure of the angle $\angle CDE$ ?