/* be name khoda */
#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
#define forifrom(i, s, n) for (ll i = s; i < n; ++i)
#define fori(i, n) forifrom(i, 0, n)
#define forirto(i, n, e) for (ll i = (n) - 1; i >= e; --i)
#define forir(i, n) forirto(i, n, 0)
#define smin(a, b) a = min(a, b)
// ------------------------------------------------------------------
const ll INF = 4340410370284600380LL;
const ll maxn = 210;
ll N, L, X[maxn], T[maxn], dp[maxn][maxn][maxn][2];
// dp[k][l][r][2] -> minimum time to get k stamps
void update(ll k, ll l, ll r, ll b, ll a) {
smin(dp[k][l][r][b], a);
if (b == 0 && T[l] >= a || b == 1 && T[r] >= a) smin(dp[k + 1][l][r][b], a);
}
int main() {
ios::sync_with_stdio(false), cin.tie(0), cout.tie(0);
//ifstream cin("3.in");
cin >> N >> L;
fori (i, N) cin >> X[i + 1];
fori (i, N) cin >> T[i + 1];
X[N + 1] = L;
memset(dp, 60, sizeof dp);
ll ans = 0;
dp[0][0][N + 1][0] = dp[0][0][N + 1][1] = 0;
fori (k, N + 1) {
forirto (t, N + 2, 1) {
fori (l, N - t + 2) {
ll r = l + t;
ll vl = dp[k][l][r][0], vr = dp[k][l][r][1];
if (vl < INF) {
ans = k;
update(k, l + 1, r, 0, vl + X[l + 1] - X[l]);
update(k, l, r - 1, 1, vl + X[l] + L - X[r - 1]);
}
if (vr < INF) {
ans = k;
update(k, l, r - 1, 1, vr + X[r] - X[r - 1]);
update(k, l + 1, r, 0, vr + L - X[r] + X[l + 1]);
}
}
}
}
cout << ans << '\n';
}
