#include <bits/stdc++.h>
#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp>
#define ll long long
#define ld long double
#define ull unsigned long long
#define ff first
#define ss second
#define pii pair<int,int>
#define pll pair<long long, long long>
#define vi vector<int>
#define vl vector<long long>
#define pb push_back
#define rep(i, b) for(int i = 0; i < (b); ++i)
#define rep2(i,a,b) for(int i = a; i <= (b); ++i)
#define rep3(i,a,b,c) for(int i = a; i <= (b); i+=c)
#define count_bits(x) __builtin_popcountll((x))
#define all(x) (x).begin(),(x).end()
#define siz(x) (int)(x).size()
#define forall(it,x) for(auto& it:(x))
using namespace __gnu_pbds;
using namespace std;
typedef tree<int, null_type, less<int>, rb_tree_tag,tree_order_statistics_node_update> ordered_set;
//mt19937 mt;void random_start(){mt.seed(chrono::time_point_cast<chrono::milliseconds>(chrono::high_resolution_clock::now()).time_since_epoch().count());}
//ll los(ll a, ll b) {return a + (mt() % (b-a+1));}
const int INF = 1e9+50;
const ll INF_L = 1e18+40;
const ll MOD = 1e9+7;
ll dp[202][202][202][2];
int poz[201];
ll time_[201];
int main()
{
ios_base::sync_with_stdio(0);cin.tie(0);cout.tie(0);
//random_start();
int n;
ll L;
cin >> n >> L;
rep2(i,0,n)
{
rep2(j,0,n)
{
rep2(k,0,n)
{
rep(d,2)
{
dp[i][j][k][d] = 1e18;
}
}
}
}
rep2(i,1,n) cin >> poz[i];
rep2(i,1,n) cin >> time_[i];
dp[(time_[1] >= poz[1] ? 1 : 0)][1][0][0] = poz[1];
dp[(time_[n] >= L-poz[n] ? 1 : 0)][0][1][1] = L-poz[n];
rep2(ans,0,n)
{
rep2(pref,0,n)
{
rep2(suf,0,n)
{
if(pref+suf >= n) break;
ll v0 = dp[ans][pref][suf][0];
ll v1 = dp[ans][pref][suf][1];
if(pref != 0) dp[ans + (time_[pref+1] >= v0 + poz[pref+1] - poz[pref])][pref+1][suf][0] = min(dp[ans + (time_[pref+1] >= v0 + poz[pref+1] - poz[pref])][pref+1][suf][0],v0+poz[pref+1]-poz[pref]);
if(suf != 0) dp[ans + (time_[pref+1] >= v1 + L-poz[n-suf+1] + poz[pref+1])][pref+1][suf][0] = min(dp[ans + (time_[pref+1] >= v1 + L-poz[n-suf+1] + poz[pref+1])][pref+1][suf][0],v1 + L-poz[n-suf+1] + poz[pref+1]);
if(pref != 0) dp[ans + (time_[n-suf] >= v0 + poz[pref] + L - poz[n-suf])][pref][suf+1][1] = min(dp[ans + (time_[n-suf] >= v0 + poz[pref] + L - poz[n-suf])][pref][suf+1][1], v0 + poz[pref] + L - poz[n-suf]);
if(suf != 0) dp[ans + (time_[n-suf] >= v1 + poz[n-suf+1] - poz[n-suf])][pref][suf+1][1] = min(dp[ans + (time_[n-suf] >= v1 + poz[n-suf+1] - poz[n-suf])][pref][suf+1][1],v1 + poz[n-suf+1] - poz[n-suf]);
}
}
}
int ans = 0;
rep2(ans2,0,n)
{
rep2(pref,0,n)
{
rep2(suf,0,n)
{
rep(d,2)
{
if(dp[ans2][pref][suf][d] != 1e18)
{
ans = max(ans,ans2);
}
}
}
}
}
cout << ans << "\n";
}
