from math import gcd
import functools
def solve(lst):
    lst.sort()
    bla = functools.reduce(gcd,[x - lst[i] for i,x in enumerate(lst[1:])])
    return bla - lst[0]%bla if lst[0]%bla != 0 else 0
f = open('small.in', 'r')
for case in range(int(f.readline())):
    print('Case #{:d}: {:d}'.format(case +1, int(solve(list(map(int,f.readline().split()[1:]))))))