Probability is based on all the results. The first person is 1/5, as everyone knows. But if the first person smokes, the possibility of the second person smoking is 0; If the first person doesn't smoke, the possibility of the second person smoking is 1/4, so the total probability is still1/5 * 0+(1-kloc-0//5) *1/4 =1/5. The same is true below.
You didn't draw the first four. This is not all the possibilities, just the probability of someone in a certain situation. So I can't count like you.