kazu,sozai =  map(int,input().split())

for i in kazu:

    titi = max(int(sozai))
    haha = min(int(sozai))

    int(sozai).remove(titi)
    int(sozai).remove(haha)

    son = (titi + haha)/2 

    sozai.add(str(son))

print(str(sozai))

