#include <bits/stdc++.h>
using namespace std;
using ll = long long;
using vll = vector<ll>;
using vi = vector<int>;
using vvi = vector<vector<int>>;
using vvl = vector<vector<ll>>;
const int N = 205;
const ll INF = 1e18;
ll dp[N][N][N][2];
void tkmin(ll &a, ll b) { a = min(a, b); }
int main() {
ios::sync_with_stdio(false);
cin.tie(0);
for (int i = 0; i < N; i++) {
for (int j = 0; j < N; j++) {
for (int k = 0; k < N; k++) {
dp[i][j][k][0] = INF;
dp[i][j][k][1] = INF;
}
}
}
int n, l; cin >> n >> l;
vll v(n);
vll t(n);
for (auto &it: v) cin>>it;
for (auto &it: t) cin>>it;
vll v2 = v;
reverse(v2.begin(), v2.end());
for (auto &it: v2) it = l-it;
v.insert(v.begin(), 0);
v2.insert(v2.begin(), 0);
vll t2 = t;
reverse(t2.begin(), t2.end());
t.insert(t.begin(), 0);
t2.insert(t2.begin(), 0);
dp[0][0][0][0] = 0;
for (int i = 0; i < n; i++) {
for (int j = 0; j+i < n; j++) {
for (int cnt = 0; cnt < n; cnt++) {
// right side
ll cur = dp[i][j][cnt][0];
ll dist = v[i+1] - v[i];
ll ncnt = cnt;
if (cur + dist <= t[i+1]) ncnt++;
tkmin(dp[i+1][j][ncnt][0], cur + dist);
dist = v2[j+1] + v[i];
ncnt = cnt;
if (cur + dist <= t2[j+1]) ncnt++;
tkmin(dp[i][j+1][ncnt][1], cur + dist);
// at left side
cur = dp[i][j][cnt][1];
dist = v2[j+1] - v2[j];
ncnt = cnt;
if (cur + dist <= t2[j+1]) ncnt++;
// if (cnt == 4 && i == 2 && j == 2) cout << ncnt << ' ' << dp[i][j+1][ncnt][1] << '\n';
tkmin(dp[i][j+1][ncnt][1], cur + dist);
// if (cnt == 4 && i == 2 && j == 2) cout << dp[i][j+1][ncnt][1] << '\n';
dist = v2[j] + v[i+1];
ncnt = cnt;
if (cur + dist <= t[i+1]) ncnt++;
tkmin(dp[i+1][j][ncnt][0], cur + dist);
}
}
}
ll ans = 0;
for (int cnt = 0; cnt <= n; cnt++) {
// cout << cnt <<": \n";
for (int i = 0; i <= n; i++) {
for (int j = 0; j+i <= n; j++) {
// auto p = [] (ll x) { return x >= INF? -1: x; };
// cout << p(dp[i][j][cnt][0]) << ":" << p(dp[i][j][cnt][1]) << ' ';
if (dp[i][j][cnt][0] != INF || dp[i][j][cnt][1] != INF) ans = cnt;
}
// cout << '\n';
}
// cout << '\n';
}
cout << ans << '\n';
return 0;
}
/*
alias csafe='g++ -std=c++17 -Wshadow -Wall -DLOCAL -fsanitize=address -fsanitize=undefined -D_GLIBCXX_DEBUG -g'
*/
