#ifndef LOCAL
#include "shortcut.h"
#endif
#include <bits/stdc++.h>
using namespace std;
#define int long long
const int maxn=3005;
int X[maxn];
vector<int32_t> L, D;
int C;
int n;
const int oo = 1'000'000'000'000'000'000ll;
typedef pair<int,int>pi;
int c1[maxn],c2[maxn];
struct node{
int tree[4*maxn];
void update(int node, int s, int e, int x, int nval){
if(s==e){
tree[node]=nval;
return;
}
int m=(s+e)/2;
if(x<=m)update(node<<1,s,m,x,nval);
else update(node<<1|1,m+1,e,x,nval);
tree[node]=max(tree[node<<1],tree[node<<1|1]);
}
int query(int node, int s, int e, int x, int y){
if(s==x&&e==y)return tree[node];
int m=(s+e)/2;
if(x>m)return query(node<<1|1,m+1,e,x,y);
else if(y<=m)return query(node<<1,s,m,x,y);
else return max(query(node<<1,s,m,x,m),query(node<<1|1,m+1,e,m+1,y));
}
} seg1,seg2;
int get(int L, int R){
int dl=0,dr=0;
for(int i=0;i<=L;i++)dl=max(dl,-X[i]+D[i]);
for(int i=R;i<n;i++)dr=max(dr,X[i]+D[i]);
int ans=0;
ans=max(ans,dl+dr+min(X[R]-X[L],C)+X[L]-X[R]);
int m1=0;
for(int i=L+1;i<=R;i++){
m1=max(m1,D[i] + min(X[i]-X[L], X[R]-X[i]+C));
}
ans=max(ans,m1 + dl+X[L]);
int m2=0;
for(int i=L;i<R;i++){
m2=max(m2,D[i] + min(X[R]-X[i], X[i]-X[L]+C));
}
ans=max(ans,m2+dr-X[R]);
int bet=0;
int idx=L;
for(int i=L;i<=R;i++){
c1[i]=-X[i]+D[i];
c2[i]=X[i]+D[i];
seg1.update(1,0,n,i,c1[i]);
seg2.update(1,0,n,i,c2[i]);
}
for(int i=L+1;i<=R;i++){
int lo = L-1, hi=i;
while(lo<hi-1){
int mi=(lo+hi)/2;
int c1= D[i] + D[mi] + X[i] - X[mi]; // walk
int c2 = D[i] + D[mi] + C + X[mi] - X[L] + X[R] - X[i]; // teleport
if(c2<=c1){
lo=mi;
} else{
hi=mi;
}
}
//[lo,i] teleport
//[lo+1,i] walk
if(L<=lo){
int wst=seg2.query(1,0,n,L,lo);
bet=max(bet,D[i] - X[i] - X[L] + X[R] + wst);
}
if(lo+1<=i-1){
int wst=seg1.query(1,0,n,lo+1,i-1);
bet=max(bet,D[i] + X[i] + wst);
}
}
ans=max(ans,bet);
for(int i=L;i<=R;i++){
for(int j=i+1;j<=R;j++){
bet=max(bet,D[i]+D[j]+min(X[j]-X[i],C+X[i]-X[L]+X[R]-X[j]));
}
}
ans=max(ans,bet);
vector<pi> vm1,vm2;
for(int i=0;i<=L;i++){
vm1.push_back({X[i]+D[i],i});
vm2.push_back({-X[i]+D[i],i});
}
sort(vm1.begin(),vm1.end(),greater<pi>());
sort(vm2.begin(),vm2.end(),greater<pi>());
for(int i=0;i<=min(1ll,(int)vm1.size()-1);i++){
for(int j=0;j<=min(1ll,(int)vm2.size()-1);j++){
if(vm1[i].second != vm2[j].second){
ans=max(ans,vm1[i].first+vm2[j].first);
}
}
}
vm1.clear();
vm2.clear();
for(int i=R;i<n;i++){
vm1.push_back({X[i]+D[i],i});
vm2.push_back({-X[i]+D[i],i});
}
sort(vm1.begin(),vm1.end(),greater<pi>());
sort(vm2.begin(),vm2.end(),greater<pi>());
for(int i=0;i<=min(1ll,(int)vm1.size()-1);i++){
for(int j=0;j<=min(1ll,(int)vm2.size()-1);j++){
if(vm1[i].second != vm2[j].second){
ans=max(ans,vm1[i].first+vm2[j].first);
}
}
}
return ans;
}
long long find_shortcut(int32_t n, vector<int32_t> l, vector<int32_t> d, int32_t c)
{
L=l;D=d;C=c;
::n=n;
for(int i=1;i<n;i++){
X[i]=X[i-1]+l[i-1];
}
int ans=oo;
for(int i=0;i<n;i++){
vector<int> vec;
for(int j=i+1;j<n;j++){
int res=get(i,j);
vec.push_back(res);
ans=min(ans,res);
}
}
return ans;
}
#ifdef LOCAL
int32_t main()
{
int32_t n, c;
assert(2 == scanf("%d%d", &n, &c));
std::vector<int32_t> l(n - 1);
std::vector<int32_t> d(n);
for (int i = 0; i < n - 1; i++)
assert(1 == scanf("%d", &l[i]));
for (int i = 0; i < n; i++)
assert(1 == scanf("%d", &d[i]));
long long t = find_shortcut(n, l, d, c);
printf("%lld\n", t);
return 0;
}
#endif
