#include <bits/stdc++.h>
using namespace std;
map<int, int> mp;
set<int> x;
multiset<int> y;
int l;
vector<vector<vector<vector<int>>>> dp;
int recurse(int cur, int t, bool w, bool s, int ll, int rr) {
if (x.empty() || *--y.end() < t) return 0;
if (dp[w][s][ll][rr] != -1) return dp[w][s][ll][rr];
bool k;
int p, cost, g;
set<int>::iterator it;
it = x.upper_bound(cur);
k = 0;
if (it == x.begin()) k = 1, it = --x.end();
else --it;
p = *it;
x.erase(p);
y.erase(y.find(mp[p]));
cost = (k ? cur + l - p : cur - p);
g = (t + cost <= mp[p]) + recurse(p, t + cost, 0, 0, ll + 1, rr);
x.insert(p);
y.insert(mp[p]);
it = x.upper_bound(cur);
k = 0;
if (it == x.end()) k = 1, it = x.begin();
p = *it;
cost = (k ? l - cur + p : p - cur);
x.erase(p);
y.erase(y.find(mp[p]));
g = max(g, (t + cost <= mp[p]) + recurse(p, t + cost, 0, 1, ll, rr + 1));
x.insert(p);
y.insert(mp[p]);
dp[0][s][ll][rr] = g;
it = x.upper_bound(cur);
k = 0;
if (it == x.end()) k = 1, it = x.begin();
p = *it;
cost = (k ? l - cur + p : p - cur);
x.erase(p);
y.erase(y.find(mp[p]));
g = (t + cost <= mp[p]) + recurse(p, t + cost, 1, 1, ll, rr + 1);
x.insert(p);
y.insert(mp[p]);
it = x.upper_bound(cur);
k = 0;
if (it == x.begin()) k = 1, it = --x.end();
else --it;
p = *it;
x.erase(p);
y.erase(y.find(mp[p]));
cost = (k ? cur + l - p : cur - p);
g = max(g, (t + cost <= mp[p]) + recurse(p, t + cost, 1, 0, ll + 1, rr));
x.insert(p);
y.insert(mp[p]);
dp[1][s][ll][rr] = g;
return max(dp[0][s][ll][rr], dp[1][s][ll][rr]);
}
int main() {
ios_base::sync_with_stdio(false);
cin.tie(0);
int n;
cin >> n >> l;
for (int i = 0; i < n; i++) {
int k;
cin >> k;
x.insert(k);
}
dp = vector (2, vector(2, vector (n, vector<int> (n, -1))));
for (auto k : x) cin >> mp[k], y.insert(mp[k]);
cout << recurse(0, 0, 0, 0, 0, 0) << '\n';
}
