In a classroom, there are 5 students. The ages of the students are compared as follows: The 1st student is 15 years old. The 2nd student is 3 years younger than the 1st student. The 3rd student is 2 years older than the 2nd student. The 4th student is half the age of the 3rd student, and the 5th student is 4 times the age of the 4th student. What is the average age of all the students? Let's think step by step and output the final answer within \boxed{}.
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