#include <bits/stdc++.h>
using namespace std;
#define rep(i, x, limit) for (long long i = (long long)x; i < (long long)limit; i++)
#define REP(i, x, limit) for (long long i = (long long)x; i <= (long long)limit; i++)
#define all(x) x.begin(), x.end()
#define rall(x) x.rbegin(), x.rend()
#define el '\n'
#define spa " "
#define Yes cout << "Yes" << el
#define No cout << "No" << el
#define YES cout << "YES" << el
#define NO cout << "NO" << el
#define eps (1e-10)
#define Equals(a,b) (fabs((a) - (b)) < eps )
#define debug(x) cerr << #x << " = " << x << el
using ll = long long;
using ull = unsigned long long;
using pii = pair<int,int>;
using pll = pair<ll,ll>;
using vi = vector<int>;
using vl = vector<ll>;
using vvl = vector<vector<ll>>;
using vs = vector<string>;
using vb = vector<bool>;
const double pi = 3.141592653589793238;
const int inf = 1073741823;
const ll infl = 1LL << 60;
const string ABC = "ABCDEFGHIJKLMNOPQRSTUVWXYZ";
const string abc = "abcdefghijklmnopqrstuvwxyz";
const ll MOD = 998244353;
#include<atcoder/all>
using namespace atcoder;
using mint = modint998244353;
using vm = vector<mint>;

int main() {
  ios::sync_with_stdio(false);
  cin.tie(nullptr);
  ll n,h;cin>>n>>h;
  vl A(n),B(n);
  rep(i,0,n)cin>>A[i];
  rep(i,0,n)cin>>B[i];
  vl As=A;
  rep(i,1,n){
    As[i]+=As[i-1];
  }
  vl Bs=B;
  rep(i,0,n-1){
    Bs[n-2-i]+=Bs[n-1-i];
  }
  vl Bss=Bs;
  rep(i,0,n-1){
    Bss[n-2-i]+=Bss[n-1-i];
  }
  ll ans=0;
  auto Cal=[&](ll l,ll r){
    ll res=Bss[l]-(r+1<n?Bss[r+1]:0)-(r+1<n?Bs[r+1]*(r-l+1):0);
    return res;
  };
  auto Cal1=[&](ll l,ll r){
    return Cal(l,r)<=h;
  };
  rep(i,0,n){
    ll l=i-1,r=n;
    while(r-l>1){
      ll m=(l+r)/2;
      if(Cal1(i,m))l=m;
      else r=m;
    }
    if(l<i)continue;
    ans=max(ans,As[l]-(i>0?As[i-1]:0));
  }
  cout<<ans<<el;
}