#include <bits/stdc++.h>
using namespace std;
#define int long long
map<int, int> mp;
set<int> x;
multiset<int> y;
int l;
vector<vector<vector<pair<int, int>>>> dp;
int recurse(int cur, int t, bool s, int ll, int rr) {
if (x.empty() || *--y.end() < t) return 0;
if (dp[s][ll][rr].first < t) return dp[s][ll][rr].second;
auto it = x.upper_bound(cur);
int k = 0;
if (it == x.end()) k = 1, it = x.begin();
int p = *it;
int cost = (k ? l - cur + p : p - cur);
x.erase(p);
y.erase(y.find(mp[p]));
int g = (t + cost <= mp[p]) + recurse(p, t + cost, 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, 0, ll + 1, rr));
x.insert(p);
y.insert(mp[p]);
if (g == dp[s][ll][rr].second) dp[s][ll][rr] = min(dp[s][ll][rr], {t, g});
else if (g > dp[s][ll][rr].second) dp[s][ll][rr] = {t, g};
return dp[s][ll][rr].second;
}
signed 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<vector<vector<pair<int, int>>>> (2, vector<vector<pair<int, int>>> (n, vector<pair<int, int>> (n, {1e18, 0})));
for (auto k : x) cin >> mp[k], y.insert(mp[k]);
cout << recurse(0, 0, 0, 0, 0) << '\n';
}
