#include <bits/stdc++.h>
#pragma GCC target("avx2")
#pragma GCC optimize("O3,unroll-loops")
using namespace std;
#define int long long
#define pii pair<int,int>
#define ff first
#define ss second
#define sp << " " <<
#define all(cont) cont.begin(),cont.end()
#define vi vector<int>
const int inf = 1e17,N = 2e6+1,MOD = (1LL<<61)-1,B = 23;
void mn(int& a,int b) {
a = min(a,b);
}
void solve() {
int n,L;
cin >> n >> L;
vi x(n+2,0),d(n+1);
for (int i=1;i<=n;i++) cin >> x[i];
for (int i=1;i<=n;i++) cin >> d[i];
x[n+1] = L;
int dp[n+1][n+1][n+1][2];
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] = dp[i][j][k][1] = inf;
dp[0][0][0][0] = dp[0][0][0][1] = 0;
for (int t = 0; t < n;t++) {
for (int l = 0;l<=t;l++) {
int r = t-l;
int sol = x[n-l+1];
int sag = x[r];
int nxtsol = x[n-l];
int nxtsag = x[r+1];
for (int k = 0;k<=t;k++) {
if (dp[l][r][k][0] != inf) {
//soldayım
mn(dp[l+1][r][k+((sol-nxtsol)+dp[l][r][k][0] <= d[n-l])][0],dp[l][r][k][0]+(sol-nxtsol));
mn(dp[l][r+1][k+((L-sol)+(nxtsag)+dp[l][r][k][0] <= d[r+1])][1],dp[l][r][k][0]+(L-sol)+(nxtsag));
}
if (dp[l][r][k][1] != inf) {
mn(dp[l][r+1][k+((nxtsag-sag)+dp[l][r][k][1] <= d[r+1])][1],dp[l][r][k][1]+(nxtsag-sag));
mn(dp[l+1][r][k+((sag)+(L-nxtsol)+dp[l][r][k][1] <= d[n-l])][0],dp[l][r][k][1]+(sag)+(L-nxtsol));
}
}
}
}
int ans = 0;
for (int s = 0;s <= n;s++) {
for (int j = 0;j<=n;j++) {
if (dp[s][n-s][j][0] != inf || dp[s][n-s][j][1] != inf) {
ans = max(ans,j);
}
}
}
cout << ans << '\n';
}
int32_t main() {
ios_base::sync_with_stdio(0);cin.tie(0);cout.tie(0);
#ifdef Dodi
freopen("in.txt","r",stdin);
freopen("out.txt","w",stdout);
#endif
int t = 1;
//cin >> t;
while (t --> 0) solve();
}
