n, m = map(int, input().split())
A = list(map(int, input().split()))
B = list(map(int, input().split()))
C = [(a - b) % m for a, b in zip(A, B)]
b = 0
D = []
for c in C:
    D.append((c - b) % m)
    b = c
D.append((-b) % m)
D.sort()
tot = sum(D)
tot2 = 0
ans = tot
for d in D[::-1]:
    tot2 += m - d
    tot -= d
    ans = min(ans, max(tot, tot2))
print(ans)