import bisect

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

s.sort()
t.sort()
burden = 0
used = [False] * n  

si = 0 

for tj in t:
    i = bisect.bisect_left(s, tj, si)
    while i < n and used[i]:
        i += 1
    if i >= n:
        break
    burden = max(burden, s[i] - tj)
    used[i] = True
    si = i + 1 

print(burden)