Given :

A die is rolled initially

If even number occurs on the die,a coin is tossed once

If odd number occurs on the die,a coin is tossed twice.

Therefore,the sample space can be written as

$S=\left\{\begin{array}{1 1}1HH,1HT,1TH,1TT,2H,2T,\\3HH,3HT,3TH,3TT,4H,4T,\\5HH,5HT,5TH,5TT,6H,6T\end{array}\right\}$