#include <map>
#include <queue>
#include <cstdio>
#include <cstring>
#include <algorithm>
const int N = 1e6 + 10;
typedef long long ll;
map<int, int> id;

struct edge {
    int v, next, w;
} E[N << 3];

int p[N << 3], cnt;

inline void init() {
    memset(p, -1, sizeof (p));
    cnt = 0;
}

inline void insert(int u, int v, int w) {
    E[cnt].w = w;
    E[cnt].v = v;
    E[cnt].next = p[u];
    p[u] = cnt++;
}

int a[N], b[N], st[N], vis[N], tn, tp;
ll dis[N];

priority_queue<pair<ll, int> > pq;

ll Dij(int s, int t) {
    memset(dis, 0x3f, sizeof (dis));
    dis[s] = 0;
    pq.emplace(-dis[s], s);
    while (!pq.empty()) {
        auto r = pq.top();
        pq.pop();
        int u = r.second;
        if (vis[u]) continue;
        vis[u] = 1;
        for (int i = p[u], v; i + 1; i = E[i].next) {
            v = E[i].v;
            if (dis[v] > dis[u] + E[i].w) {
                dis[v] = dis[u] + E[i].w;
                pq.emplace(-dis[v], v);
            }
        }
    }
    return dis[t];
}

int main() {
    init();
    int n, m;
    scanf("%d%d", &n, &m);
    tn = n;

    for (int i = 1; i <= n; ++i) {
        scanf("%d", &a[i]);
        if (!id[m - a[i]]) id[m - a[i]] = ++tn, st[++tp] = m - a[i];
        insert(i, id[m - a[i]], 0);
    }

    for (int i = 1; i <= n; ++i) {
        scanf("%d", &b[i]);
        if (!id[b[i]]) id[b[i]] = ++tn, st[++tp] = b[i];
        insert(id[b[i]], i, 0);
    }

    sort(st + 1, st + tp + 1);

    for (int i = 1; i < tp; ++i) insert(id[st[i]], id[st[i + 1]], (st[i + 1] - st[i]) % m);

    insert(id[st[tp]], id[st[1]], (m + st[1] - st[tp]) % m);

    printf("%lld\n", Dij(1, n));
    return 0;
}