N = input()
Xs = map(int, raw_input().split())

if N < 2: 
    ans = 0

else:
    ans = max(Xs)
    for x in Xs:
        for i in range(1, max(Xs)):
            if i > ans: break
            elif (x + i) in Xs or (x - i) in Xs:
                if ans >= i:
                    ans = i

print ans