def Gcd(a, b):
  if b == 0:
    return a
  return Gcd(b, a % b)

def Solve(L):
  y = L[0]
  L1 = [abs(x - y) for x in L]
  g = reduce(Gcd, L1)
  if y % g == 0:
    return 0
  else:
    return g - (y % g)

with open('B-large-practice.in') as f:
  lines = f.readlines()

with open('B-large-practice.out', 'w') as output:
  N = int(lines[0])
  for testcase, i in enumerate(range(N)):
    codes = map(int,lines[i+1].split())
    output.write("Case #%d: %d\n" % (testcase+1, Solve(codes[1:])))