RMO paper crease

A square sheet of paper ABCD is so folded that B falls on the midpoint M of CD. Find the ratio in which the crease will divide BC. If your answer is the form $x$ $\frac{y}{z}$ ,where $y$ < $z$ and $y$ and $z$ are coprime. Give your answer as $x+y+z$ .

Source : RMO 1990