#include<bits/stdc++.h>
#define int long long
#define all(v) v.begin(), v.end()
#define SZ(x) (int)x.size()
#define pii pair<int, int>
#define X first
#define Y second
using namespace std;
const int maxn = 2e5 + 10;
const int mod = 1e9 + 7;// 998244353;
const int llmx = 1e18;
int dis[2][201][201][201];
void sol(){
int n, L;
cin >> n >> L;
vector< int > x(n + 1);
vector< int > t(n + 1, -1);
for(int i = 1; i <= n; ++i) cin >> x[i];
for(int i = 1; i <= n; ++i) cin >> t[i];
int ans = 0;
priority_queue< array<int, 5>, vector< array<int, 5> >, greater< array<int, 5> > > pq;
for(int f : {0, 1}) for(int i = 0; i <= n; ++i) for(int j = 0; j <= n; ++j) for(int k = 0; k <= n; ++k) dis[f][i][j][k] = llmx;
dis[0][0][0][0] = 0, dis[1][0][0][0] = 0;
pq.push({0, 0, 0, 0, 0});
pq.push({0, 1, 0, 0, 0});
auto F = [&](int l, int r) -> int {
return min(abs(x[r] - x[l]), L - abs(x[r] - x[l]));
};
while(!pq.empty()){
auto [D, f, l, r, ct] = pq.top(); pq.pop();
// cerr << D << " " << f << " " << l << " " << r << " " << ct << "!!\n";
// L : 0, R : 1
int nl = (l + n) % (n + 1);
int nr = (r + 1) % (n + 1);
ans = max(ans, ct);
if(nl != r){
int tim = D + F(f ? r : l, nl);
int nct = ct + (tim <= t[nl]);
if(dis[0][nl][r][nct] > tim){
dis[0][nl][r][nct] = tim;
pq.push({dis[0][nl][r][nct], 0, nl, r, nct});
}
}
if(nr != l){
int tim = D + F(f ? r : l, nr);
int nct = ct + (tim <= t[nr]);
if(dis[1][l][nr][nct] > tim){
dis[1][l][nr][nct] = tim;
pq.push({dis[1][l][nr][nct], 1, l, nr, nct});
}
}
}
cout << ans << "\n";
}
/*
6 25
3 4 7 17 21 23
11 7 17 10 8 10
// 4
5 20
4 5 8 13 17
18 23 15 7 10
// 5
4 19
3 7 12 14
2 0 5 4
// 0
10 87
9 23 33 38 42 44 45 62 67 78
15 91 7 27 31 53 12 91 89 46
// 5
*/
signed main(){
ios::sync_with_stdio(0), cin.tie(0), cerr.tie(0);
int t = 1; //cin >> t;
while(t--) sol();
}
