#include<bits/stdc++.h>
using namespace std;
const long long MX = 220;
long long t[MX], x[MX], ans;
long long dp[MX][MX][MX][2];
void update(long long l,long long r,long long k,long long side,long long time)
{
long long zar=((side==0)?l:r);
k+=(t[zar]>=time);
ans=max(ans,k);
dp[l][r][k][side]=(((dp[l][r][k][side]==-1)|(dp[l][r][k][side]>time))?time:dp[l][r][k][side]);
}
int main()
{
cin.tie(0);
ios_base::sync_with_stdio(0);
long long n, rd;
cin>>n>>rd;
for(long long i = 1; i <= n; i++)
cin>>x[i];
for(long long i = 1; i <= n; i++)
cin>>t[i];
memset(dp, -1, sizeof(dp));
update(1, n, 0, 0, x[1]);
update(1, n, 0, 1, rd - x[n]);
for(long long i = 1; i <= n; i++)
{
for(long long j = 1; j <= i; j++)
{
for(long long k = 0; k <= i; k++)
{
long long l = j;
long long r = n - i + j;
if(l >= r)
{
continue;
}
if(dp[l][r][k][0] != -1)
{
update(l+1, r, k, 0, dp[l][r][k][0] + x[l+1] - x[l]);
update(l+1, r, k, 1, dp[l][r][k][0] + x[l] + rd - x[r]);
}
if(dp[l][r][k][1] != -1)
{
update(l, r-1, k, 1, dp[l][r][k][1] + (x[r] - x[r-1]));
update(l, r-1, k, 0, dp[l][r][k][1] + (rd - x[r] + x[l]));
}
}
}
}
cout<<ans<<'\n';
}
