#include <bits/stdc++.h>
using namespace std;
#define ll long long
#define ull unsigned long long
#define pb(e) push_back(e)
#define sv(a) sort(a.begin(),a.end())
#define sa(a,n) sort(a,a+n)
#define mp(a,b) make_pair(a,b)
#define vf first
#define vs second
#define ar array
#define all(x) x.begin(),x.end()
const int inf = 0x3f3f3f3f;
const int mod = 1000000007;
const double PI=3.14159265358979323846264338327950288419716939937510582097494459230;
bool remender(ll a , ll b){return a%b;}
void solve(){
int n;
ll l;
cin >> n >> l;
ll arr[n];
for(int i = 0; i < n; i++)cin >> arr[i];
ll t[n];
for(int i = 0; i < n; i++)cin >> t[i];
queue<vector<int>> q;
// i , j , taken, place
q.push({n-1,0,0,0});
q.push({n-1,0,0,1});
ll dp[n + 1][n + 1][n + 1][2];
bool vis[n + 1][n + 1][n + 1][2];
memset(vis,0,sizeof vis);
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] = 1e18;
}
}
dp[n-1][0][0][0] = dp[n-1][0][0][1] = 0;
int ans = 0;
int lol = 0;
while(q.size()){
vector<int> v = q.front();
q.pop();
int i = v[0] , j = v[1];
ll time = dp[i][j][v[2]][v[3]];
lol++;
if((i + 1) % n == j && lol > 2){
ans = max(ans , v[2]);
continue;
}
if(v[3] == 0){
int nexti = (i + 1) % n;
ll dis = 0;
if(i == n-1)dis = arr[nexti];
else dis = arr[nexti] - arr[i];
int t1 = v[2];
if(time + dis <= t[nexti])t1++;
dp[nexti][j][t1][0] = min(dp[nexti][j][t1][0] , dis + time);
if(!vis[nexti][j][t1][0]){
q.push({nexti,j,t1,0});
vis[nexti][j][t1][0] = 1;
}
int nextj = (j + n - 1) % n;
if(i == n-1)dis = l - arr[nextj];
else dis = arr[i] + (l - arr[nextj]);
t1 = v[2];
if(time + dis <= t[nextj])t1++;
dp[i][nextj][t1][1] = min(dp[i][nextj][t1][1] , dis + time);
if(!vis[i][nextj][t1][1]){
q.push({i , nextj , t1 , 1});
vis[i][nextj][t1][1] = 1;
}
}
else {
int nexti = (i + 1) % n;
ll dis =arr[nexti] + (j == 0 ? 0 : l - arr[j]);
int t1 = v[2];
if(time + dis <= t[nexti])t1++;
dp[nexti][j][t1][0] = min(dp[nexti][j][t1][0] , dis + time);
if(!vis[nexti][j][t1][0]){
q.push({nexti,j,t1,0});
vis[nexti][j][t1][0] = 1;
}
int nextj = (j + n - 1) % n;
if(j == 0)dis = l - arr[nextj];
else dis = (arr[j] - arr[nextj]);
t1 = v[2];
if(time + dis <= t[nextj])t1++;
dp[i][nextj][t1][1] = min(dp[i][nextj][t1][1] , dis + time);
if(!vis[i][nextj][t1][1]){
q.push({i , nextj , t1 , 1});
vis[i][nextj][t1][1] = 1;
}
}
}
cout << ans << '\n';
}
int main(){
ios_base::sync_with_stdio(false);
cin.tie(NULL);
//int t;cin >> t;while(t--)
solve();
return 0;
}
