PL-OM 1977 Problem 2

Let $s \geq 3$ be a given integer. A sequence $K_n$ of circles and a sequence $W_n$ of convex $s$ -gons satisfy: $$K_n \supset W_n \supset K_{n+1}$$ for all $n = 1, 2, ...$ Prove that the sequence of the radii of the circles $K_n$ converges to zero.