file = open('15A.txt')
n = int(file.readline())
A = []
for i in range(n):
    A += [int(file.readline())]

Max = 0
for i in range(n):
    for j in range(i + 1, n):
        if abs(A[i] - A[j]) % 80 == 0:
            Max = max(Max, abs(A[i] - A[j]))
print(Max)