#include <iostream>
#include <algorithm>
using namespace std;
#define int long long
const int N = 202;
int x[N], t[N], dp[N][N][N][2];
signed main(){
int n, L;
cin>>n>>L;
for (int i=1;i<=n;i++)
cin>>x[i];
for (int i=1;i<=n;i++)
cin>>t[i];
x[n+1] = L;
for (int i=0;i<=n+1;i++){
for (int j=0;j<=n+1;j++)
for (int k=0;k<=n+1;k++)
for (int l : {0, 1})
dp[i][j][k][l] = 1e17;
}
dp[0][0][n+1][0] = 0;
for (int i=0;i<=n;i++){
for (int j=0;j<n;j++){
for (int k=n+1;k > j + 1;k--){
// currently at left side
bool hit = t[j + 1] >= dp[i][j][k][0] + (x[j+1] - x[j]);
dp[i+hit][j+1][k][0] = min(dp[i+hit][j+1][k][0], dp[i][j][k][0] + (x[j+1] - x[j]));
hit = t[k - 1] >= dp[i][j][k][0] + x[j] + (L - x[k - 1]);
dp[i+hit][j][k-1][1] = min(dp[i+hit][j][k-1][1], dp[i][j][k][0] + x[j] + (L - x[k-1]));
// currently at right side
hit = t[k - 1] >= dp[i][j][k][1] + x[k] - x[k-1];
dp[i+hit][j][k-1][1] = min(dp[i+hit][j][k-1][1], dp[i][j][k][1] + x[k] - x[k-1]);
hit = t[j+1] >= dp[i][j][k][1] + L - x[k] + x[j+1];
dp[i+hit][j+1][k][0] = min(dp[i+hit][j+1][k][0], dp[i][j][k][1] + L - x[k] + x[j + 1]);
}
}
}
for (int i=n;i>=0;i--){
for (int j=0;j<=n;j++)
for (int k=n+1;k >= j + 1;k--)
for (int l : {0, 1})
if (dp[i][j][k][l] != 1e17)
return cout<<i<<endl, 0;
}
}
