In a sampling expedition near a peninsula, 180 dolphins from a large population of dolphins were captured and marked by tagging their dorsal fins. The tagged dolphins were then allowed to join back into the population. In a subsequent expedition, 42 dolphins were photographed from the same large population. Among these, 7 dolphins contained the tags. Assuming that the population size remains the same and that tags were not lost, the estimated population size of dolphins in the peninsula is ........... (answer in integer)