#include<bits/stdc++.h>
using namespace std;
const int N=210;
int n,m;
int a[N],b[N];
typedef long long LL;
LL f[N][N][N][2];
#define mn(x,y) x=min(x,y)
#define L m
int main()
{
    cin>>n>>m;
    for(int i=1;i<=n;i++)
    {
        cin>>a[i];
    }
    a[n+1]=L;
    for(int i=1;i<=n;i++)
    {
        cin>>b[i];
    }
    memset(f,0x3f,sizeof(f));
    f[0][0][0][0]=0;
    int ans=0;
    for(int len=0;len<n;len++)
    {
        for(int i=0;i<=len;i++)
        {
            int j=len-i;
            for(int k=0;k<=len;k++)
            {
                LL x=f[i][j][k][0];
                if(x<=1e9)
                {
                //    cout<<i<<' '<<j<<' '<<k<<" 0\n";
                //    cout<<x<<endl;
                    ans=max(ans,k);
                bool c=(b[(n+1-(i+1))]>=x+a[n+1-i]-a[n+1-(i+1)]);
                mn(f[i+1][j][k+c][0],x+a[n+1-i]-a[n+1-(i+1)]);
                c=(b[j+1]>=x+L-a[n+1-i]+a[j+1]);
                mn(f[i][j+1][k+c][1],x+L-a[n+1-i]+a[j+1]);
                }
                x=f[i][j][k][1];
                if(x<=1e9)
                {
                //    cout<<i<<' '<<j<<' '<<k<<" 1\n";
                //    cout<<x<<endl;
                    ans=max(ans,k);
                bool c=(b[(n+1-(i+1))]>=x+a[j]+L-a[n+1-(i+1)]);
                mn(f[i+1][j][k+c][0],x+a[j]+L-a[n+1-(i+1)]);
                c=(b[j+1]>=x+a[j+1]-a[j]);
                mn(f[i][j+1][k+c][1],x+a[j+1]-a[j]);
                }
            }
        }
    }
    cout<<ans<<'\n';
    return 0;
}