aaa = input()
bbb = raw_input().split(" ")
ccc = []
for i in bbb:
  ccc.append(float(i))

if len(ccc) % 2 == 0:
  ans = (ccc[len(ccc)/2-1]+ccc[len(ccc)/2])/2
else:
  ans = ccc[len(ccc)/2]

print ans