STAND_TOTAL, GHOST_TOTAL = map(int, input().split())
STRENGTHS = list(map(int, input().split()))
TARGETS = list(map(int, input().split()))

def main():
    STRENGTHS.sort()
    
    ok, ng = 0, GHOST_TOTAL + 1
    while abs(ok - ng) > 1:
        med = (ok + ng) // 2
        if judge(med) > -1:
            ok = med
        else:
            ng = med
    
    print(judge(ok))

def judge(x):
    if x == 0:
        return 0
        
    sub_targets = [TARGETS[case_i] for case_i in range(x)]
    sub_targets.sort()
    
    res = 0
    ghost_i = 0
    for strength in STRENGTHS:
        target = sub_targets[ghost_i]
        if strength >= target:
            ghost_i += 1
            res = max(res, strength - target)
            if ghost_i >= x:
                break
        
    if ghost_i >= x:
        return res
    else:
        return -1

if __name__ == "__main__":
    main()