n = int(input())
s = []
cha = [0]*1000001
d = 0
i=0
p=0
for _ in range(n):
    a = int(input())
    s.append(a)
for i in range(len(s)):
    for j in range(i+1, len(s)):
        cha[abs(s[i]-s[j])]=1
while True:
    i+=1
    x=1
    for j in range(i,len(cha),i):
        if cha[j]==1:
            x=0
            break
    if x == 1:
        p+=1
        print(i)
        break

#7，#9，#10，#17TLE
#11RE