#include <bits/stdc++.h>
using namespace std;
using ll = long long;
using ld = long double;
using D = double;
using uint = unsigned int;
#ifdef WIN32
#define LLD "%I64d"
#else
#define LLD "%lld"
#endif
#define pb push_back
#define mp make_pair
#define all(x) (x).begin(),(x).end()
#define fi first
#define se second
const int maxn = 3000005;
const ll inf = 1e18;
ll x[maxn], d[maxn];
int n, C;
priority_queue<pair<ll, int>, vector<pair<ll, int>>, greater<pair<ll, int>>> q;
int ans1, ans2;
bool can(ll diam)
{
// cout << "can " << diam << endl;
bool needleft = false;
ll maxsum = inf;
ll minsum = -inf;
ll maxdif = inf;
ll mindif = -inf;
pair<ll, ll> mostleft = {inf, -inf};
pair<ll, ll> mostright = {-inf, -inf};
while (!q.empty()) q.pop();
for (int i = 0; i < n; i++)
{
// no need to check whether it is "small" or not, because in case of "small" its square is inside "big"'s square
while (!q.empty() && x[i] - q.top().fi + d[i] > diam)
{
int wh = q.top().se;
q.pop();
if (x[wh] - d[wh] < mostleft.fi - mostleft.se) mostleft = {x[wh], d[wh]};
if (x[wh] + d[wh] > mostright.fi + mostright.se) mostright = {x[wh], d[wh]};
needleft = true;
}
if (needleft)
{
maxsum = min(maxsum, (mostleft.fi + diam - C - d[i] - mostleft.se) + x[i]);
minsum = max(minsum, (mostright.fi - (diam - C - d[i] - mostright.se)) + x[i]);
maxdif = min(maxdif, x[i] - (mostright.fi - (diam - C - d[i] - mostright.se)));
mindif = max(mindif, x[i] - (mostleft.fi + diam - C - d[i] - mostleft.se));
}
q.push({x[i] - d[i], i});
}
// cout << minsum << ' ' << maxsum << ' ' << mindif << ' ' << maxdif << endl;
if (maxsum < minsum || maxdif < mindif) return false;
int curdif = 0;
int cursum = n;
for (int i = 0; i < n; i++)
{
while (curdif < n && x[curdif] - x[i] < mindif) curdif++;
while (cursum > 0 && x[cursum - 1] + x[i] >= minsum) cursum--;
int cur = max({cursum, curdif, i + 1});
if (cur < n && x[cur] + x[i] <= maxsum && x[cur] - x[i] <= maxdif)
{
ans1 = i;
ans2 = cur;
return true;
}
}
return false;
}
long long find_shortcut(int N, vector <int> L0, vector <int> L, int C_)
{
n = N;
C = C_;
ll cursum = 0;
for (int i = 0; i < n; i++)
{
d[i] = L[i];
x[i] = cursum;
if (i + 1 < n) cursum += L0[i];
}
long long result = inf;
int end1 = 0;
int end2 = 1;
ll l = 0;
ll r = inf;
while (r - l > 1)
{
ll mid = (l + r) / 2;
if (can(mid)) r = mid;
else l = mid;
}
can(r);
end1 = ans1;
end2 = ans2;
result = r;
return result;
}
// BEGIN CUT
int main()
{
int n, c;
scanf("%d%d", &n, &c);
vector <int> l(n - 1);
vector <int> d(n);
for (int i = 0; i < n - 1; i++)
scanf("%d", &l[i]);
for (int i = 0; i < n; i++)
scanf("%d", &d[i]);
long long t = find_shortcut(n, l, d, c);
// BEGIN SECRET
puts("14e047d7a2907b9034950b074822b302");
// END SECRET
printf("%lld\n", t);
return 0;
}
// END CUT
