n = int(input())
l = sorted(map(int, input().split()))

l2 = []
for i in range(n-1):
    l2.append(l[i+1] - l[i])

l3 = []
for i in l2:
    if i != 0:
        l3.append(i)

l4 = []
for i in l3:
    l4.append(l3.count(i))
    
if len(set(l4)) == 1:
    print(min(l3))
else:
    print(0)