import sys

# sys.setrecursionlimit(200005)
int1 = lambda x: int(x)-1
pDB = lambda *x: print(*x, end="\n", file=sys.stderr)
p2D = lambda x: print(*x, sep="\n", end="\n\n", file=sys.stderr)
def II(): return int(sys.stdin.readline())
def LI(): return list(map(int, sys.stdin.readline().split()))
def LLI(rows_number): return [LI() for _ in range(rows_number)]
def LI1(): return list(map(int1, sys.stdin.readline().split()))
def LLI1(rows_number): return [LI1() for _ in range(rows_number)]
def SI(): return sys.stdin.readline().rstrip()
dij = [(0, 1), (-1, 0), (0, -1), (1, 0)]
# dij = [(0, 1), (-1, 0), (0, -1), (1, 0), (1, 1), (1, -1), (-1, 1), (-1, -1)]
inf = (1 << 63)-1
# inf = (1 << 31)-1
md = 10**9+7
# md = 998244353

class BitSum:
    def __init__(self, n):
        self.n = n+1
        self.table = [0]*self.n

    def add(self, i, x):
        i += 1
        while i < self.n:
            self.table[i] += x
            i += i & -i

    def sum(self, i):
        i += 1
        res = 0
        while i > 0:
            res += self.table[i]
            i -= i & -i
        return res

    def pos(self, x):
        idx = 0
        for lv in range((self.n-1).bit_length()-1, -1, -1):
            mid = idx+(1 << lv)
            if mid >= self.n: continue
            if self.table[mid] < x:
                x -= self.table[mid]
                idx += 1 << lv
        return idx

# 要素を先読みする代わりに、[0,10**6]でなくとも使える
class Cset:
    def __init__(self, aa):
        aa = set(aa)
        self.dec = tuple(sorted(aa))
        self.enc = {a: i for i, a in enumerate(self.dec)}
        self.mx = len(self.dec)
        self.size = 0
        self.bit = BitSum(self.mx+1)
        self.nums = [False]*(self.mx+1)

    def __repr__(self):
        return "["+" ".join(str(self[i]) for i in range(self.size))+"]"

    def insert(self, a):
        if a not in self.enc: return False
        a = self.enc[a]
        if a < 0 or a > self.mx or self.nums[a]: return False
        self.size += 1
        self.bit.add(a, 1)
        self.nums[a] = True
        return True

    def remove(self, value):
        if value not in self.enc: return False
        value = self.enc[value]
        if value < 0 or value > self.mx or not self.nums[value]: return False
        self.size -= 1
        self.bit.add(value, -1)
        self.nums[value] = False
        return True

    def erase(self, index):
        i = index
        if i >= self.size or i < -self.size: return False
        if i < 0: i = self.size+i+1
        else: i += 1
        a = self.bit.pos(i)
        self.size -= 1
        self.bit.add(a, -1)
        self.nums[a] = False
        return True

    def __getitem__(self, i):
        if i >= self.size or i < -self.size: return -1
        if i < 0: i = self.size+i+1
        else: i += 1
        return self.dec[self.bit.pos(i)]

    def __contains__(self, item):
        return self.nums[self.enc[item]]

    def __len__(self):
        return self.size

    def bisect_left(self, a):
        if a not in self.enc: return -1
        a = self.enc[a]
        if a < 0 or a > self.mx: return -1
        if a == 0: return 0
        return self.bit.sum(a-1)

    def bisect_right(self, a):
        if a not in self.enc: return -1
        a = self.enc[a]
        if a < 0 or a > self.mx: return -1
        return self.bit.sum(a)

n, l = LI()
xx0 = LI()
yy0 = LI()

ans = now = xx0[0]
xx = Cset(xx0+yy0)
yy = Cset(xx0+yy0)
for x in xx0[1:]: xx.insert(x)
for y in yy0: yy.insert(y)

for _ in range(n-1):
    j = yy.bisect_left(now)%len(yy)  # 一番近いお茶
    i = xx.bisect_left(yy[j])%len(xx)  # お茶後の寿司
    x = xx[i]
    j = (yy.bisect_left(x)-1)%len(yy)  # 次の寿司直前のお茶
    y = yy[j]
    ans += (y-now)%l+(x-y)%l
    xx.remove(x)
    yy.remove(y)
    now = x
    # pDB(y, x, ans, xx, yy)

ans += (yy[0]-now)%l

print(ans)