#include <bits/stdc++.h>
#include <atcoder/all>
using namespace std;
using namespace atcoder;
using ll = long long;
using ld = long double;
using mint = modint998244353;

int main() {
  ll N, H; cin >> N >> H;
  vector<ll> A(N), B(N);
  for (int i = 0; i < N; i++) cin >> A[i];
  for (int i = 0; i < N; i++) cin >> B[i];
  vector<ll> sumA(N + 1), sumB(N + 1);
  for (int i = 0; i < N; i++) {
    sumA[i + 1] = sumA[i] + A[i];
    sumB[i + 1] = sumB[i] + B[i];
  }
  int L = 0, R = 0;
  ll ans = 0;
  while (true) {
    if (R >= N) break;
    ll BB = 0;
    for (int i = 1; i <= R - L + 1; i++) {
      BB += sumB[R + 1] - sumB[L + i - 1];
    }
    if (BB <= H) {
      ans = max(ans, sumA[R + 1] - sumA[L]);
      R++;
    } else {
      L++;
      R = L;
    }
  }
  cout << ans << endl;
  return 0;
}