B-station

Near Berlandia, after an earthquake, an underwater station was partially flooded. The station consists of $N$ levels. For each level, the following information is given: W_i — the initial amount of water in the level, L_i — the maximum amount of water the level can tolerate, and P_i — the cost required by the engineering team to manually unblock the level. When a level is unblocked, all its water flows to the next level. If the water on a level exceeds L_i, the level automatically becomes unblocked. The engineering team wants to unblock the last level while minimizing their expenses. For this, they have hired you.