import bisect

n, m = map(int, input().split())
s = list(map(int, input().split()))
t = list(map(int, input().split()))

s.sort()

burden = 0
idx = 0 

for tj in t:
    i = bisect.bisect_left(s, tj, idx)
    if i >= len(s):
        break  
    burden = max(burden, s[i] - tj)
    idx = i + 1

print(burden)