  The basic social dilemma is frequently captured by a public goods game where
participants decide simultaneously whether to support a common pool or not and
after the enhanced contributions are distributed uniformly among all
competitors. What if the result of common efforts is {\it not} distributed
immediately, but it is reinvested and added to the pool for a next round? This
extension may not only result in an enhanced benefit for group members but also
opens new strategies for involved players because they may act in distinct
rounds differently. In this work we focus on the simplest case when two rounds
are considered, but the applied multiplication factors dedicated to a certain
round can be different. We show that in structured populations the winning
strategy may depend sensitively on the ratio of these factors and the last
round has a special importance to reach a fully cooperative state. We also
observe that it may pay for defectors to support the first round and after
enjoy the extra benefit of accumulated contributions. Full cooperator strategy
is only viable if the second round ensures a premium benefit of investments.
