The zoo transferred 131 birds to the safari park over the course of many days.
The zookeeper planned to send the same number of birds each day, except that there might be fewer on the last day, when he would send whatever was left. However, he mistakenly thought that there were 113 birds in total instead of 131, which caused the transfer to take 2 more days than he anticipated. Interestingly, the number of birds transferred during the last day was the same as he had originally planned.
How many birds were transferred during the last day?