def parse(inFile):
    return inFile.getInts()[1:]

from fractions import gcd

def solve(numbers):
    diffs = [abs(number-numbers[0]) for number in numbers[1:]]
    g = reduce(gcd, diffs, 0)
    return (-numbers[0]) % g

if __name__ == "__main__":
    from GCJ import GCJ
    GCJ(parse, solve, "/Users/lpebody/gcj/2010_q/", "b").run()