#include <bits/stdc++.h>
using namespace std;
#define int long long
void solve() {
int n, l;
cin >> n >> l;
vector <int> x(n), t(n);
for (int i = 0; i < n; ++i) {
cin >> x[i];
}
for (int i = 0; i < n; ++i) {
cin >> t[i];
}
int ans = 0;
int inf = 2e18;
vector <vector <vector <int>>> dp(2, vector <vector <int>> (n + 1, vector <int> (n + 1, 2e18)));
auto last = dp;
last[0][0][0] = 0;
int st = 0;
for (int i = 0; i < n; ++i) {
for (int j = 0; j <= n; ++j) {
for (int f = 0; f + j < n; ++f) {
if (last[0][j][f] != inf) {
if (j == 0) {
st = 0;
} else {
st = x[j - 1];
}
if (x[j] - st + last[0][j][f] <= t[j]) {
// cout << i << " " << j << " " << f << endl;
dp[0][j + 1][f] = min(dp[0][j + 1][f], x[j] - st + last[0][j][f]);
}
int ind = n - 1 - f;
if (l - x[ind] + st + last[0][j][f] <= t[ind]) {
dp[1][j][f + 1] = min(dp[1][j][f + 1], l - x[ind] + st + last[0][j][f]);
}
}
if (last[1][j][f] != inf) {
if (f == 0) {
st = l;
} else {
st = x[n - f];
}
if (last[1][j][f] + st - x[n - f - 1] <= t[n - f - 1]) {
// cout << i << " " << " " << j << " " << f << endl;
dp[1][j][f + 1] = min(dp[1][j][f + 1], last[1][j][f] + st - x[n - f - 1]);
}
if (last[1][j][f] + l - st + x[j] <= t[j]) {
// cout << i << " " << " " << j << " " << f << endl;
dp[0][j + 1][f] = min(dp[0][j + 1][f], last[1][j][f] + l - st + x[j]);
}
}
}
}
for (int j = 0; j <= n; ++j) {
for (int f = 0; f + j < n; ++f) {
if (f == 0) {
st = l;
} else {
st = x[n - f];
}
dp[0][j + 1][f] = min(dp[0][j + 1][f], dp[1][j][f] + l - st + x[j]);
dp[1][j][f + 1] = min(dp[1][j][f + 1], dp[1][j][f] + st - x[n - f - 1]);
if (j == 0) {
st = 0;
} else {
st = x[j - 1];
}
dp[1][j][f + 1] = min(dp[1][j][f + 1], l - x[n - f - 1] + st + dp[0][j][f]);
dp[0][j + 1][f] = min(dp[0][j + 1][f], x[j] - st + dp[0][j][f]);
}
}
bool flag = false;
for (int j = 0; j <= n; ++j) {
for (int f = 0; f + j <= n; ++f) {
// cout << "{" << dp[0][j][f] << " " << dp[1][j][f] << "} ";
if (dp[0][j][f] < inf || dp[1][j][f] < inf) {
flag = true;
}
last[0][j][f] = inf;
last[1][j][f] = inf;
}
// cout << '\n';
}
swap(last, dp);
if (flag) {
ans = i + 1;
} else {
break;
}
}
cout << ans << '\n';
}
signed main() {
cin.tie(0);
ios::sync_with_stdio(false);
solve();
}
/*
4 19
3 7 12 14
2 0 5 4
*/
