#include<bits/stdc++.h>
using namespace std;
const int MX = 203;
int n, L;
int pos[MX], T[MX];
map<tuple<int,int,int>, int>dp;
int MAXT;
int dist(int i, int j) {
int ret = abs(pos[i]-pos[j]);
return min(ret, L-ret);
}
int solve(int i, int j, int CLOCK) {
if(CLOCK>MAXT) return 0;
if(dp.count({i, j, CLOCK})) return dp[{i, j, CLOCK}];
int ret = 0;
if(i<j) {
if(i<n) ret = solve(j, i+1, CLOCK+dist(i, j));
else ret = solve(j, j, CLOCK+dist(i, j));
if(i<n) ret = max(ret, solve(i+1, j, CLOCK+dist(i, i+1)));
} else if(i>j) {
if(i>1) ret = solve(j, i-1, CLOCK+dist(j, i));
else ret = solve(j, j, CLOCK+dist(j, i));
if(i>1) ret = max(ret, solve(i-1, j, CLOCK+dist(i, i-1)));
}
ret += CLOCK<=T[i];
dp[{i, j, CLOCK}] = ret;
return ret;
}
void PlayGround() {
cin>>n>>L;
for(int i=1; i<=n; ++i) {
cin>>pos[i];
}
for(int i=1; i<=n; ++i) {
cin>>T[i];
MAXT = max(MAXT, T[i]);
}
cout << max(solve(1, n, pos[1]), solve(n, 1, L-pos[n])) << '\n';
}
int main() {
ios_base::sync_with_stdio(false);
cin.tie(NULL);
PlayGround();
return 0;
}
