Fun with circles

Let $C$ be a circle with centre $P_0$ and $AB$ be a diameter of $C$ . Suppose $P_1$ is the midpoint of the line segment $P_0B$ , $P_2$ is the midpoint of the line segment $P_1B$ and so on. Let $C_1, C_2, C_3 , \ldots$ be circles with diameters $P_0P_1,P_1P_2,P_2P_3,\ldots$ respectively. Suppose the circles $C_1, C_2, C_3, \ldots$ are all shaded. If the ratio of the area of the unshaded portion of $C$ to that of the original $C$ be expressed as $M:N$ , then find $M+N$ .