#ifdef NACHIA
#define _GLIBCXX_DEBUG
#else
#define NDEBUG
#endif
#include <iostream>
#include <string>
#include <vector>
#include <algorithm>
#include <utility>
#include <queue>
#include <array>
#include <cmath>
#include <atcoder/modint>
using i64 = long long;
using u64 = unsigned long long;
#define rep(i,n) for(i64 i=0; i<(i64)(n); i++)
#define repr(i,n) for(i64 i=(i64)(n)-1; i>=0; i--)
const i64 INF = 1001001001001001001;
const char* yn(bool x){ return x ? "Yes" : "No"; }
template<typename A> void chmin(A& l, const A& r){ if(r < l) l = r; }
template<typename A> void chmax(A& l, const A& r){ if(l < r) l = r; }
template<typename A> using nega_queue = std::priority_queue<A,std::vector<A>,std::greater<A>>;
using Modint = atcoder::static_modint<998244353>;
//#include "nachia/vec.hpp"
using namespace std;

void testcase(){
    i64 N, H; cin >> N >> H;
    vector<i64> A(N+1);
    rep(i,N){ i64 a; cin >> a; A[i+1] = A[i] + a; }
    vector<i64> B(N);
    rep(i,N) cin >> B[i];
    vector<i64> Bs(N + 1);
    rep(i,N) Bs[i+1] = Bs[i] + B[i];
    i64 ans = -INF;
    i64 r = N;
    i64 bsum = 0;
    for(i64 l=N-1; l>=0; l--){
        bsum += Bs[r] - Bs[l];
        while(bsum > H){
            bsum -= B[r-1] * (r-l);
            r--;
        }
        if(l != r) chmax(ans, A[r] - A[l]);
    }
    if(ans == -INF) ans = 0;
    cout << ans << endl;
}

int main(){
    ios::sync_with_stdio(false); cin.tie(nullptr);
    #ifdef NACHIA
    int T; cin >> T; for(int t=0; t<T; T!=++t?(cout<<'\n'),0:0)
    #endif
    testcase();
    return 0;
}