import sys
from math import sqrt, pi, sin, factorial
inp = lambda : sys.stdin.readline()[:-1]
mii = lambda x = " " : [*map(int,inp().split(x))]
mfi = lambda x = " " : [*map(float,inp().split(x))]
ii = lambda : int(inp())
for _ in range(ii()):
n = ii()
l = mfi()
for i in range(1, n - 1):
if l[i] <= (l[i-1] + l[i+1]) / 2:
continue
l[i] = (l[i-1] + l[i+1]) / 2
print(f"Case #{_+1}: {l[n - 2]}")