#include <bits/stdc++.h>
using namespace std;

int const N = 1000000;

typedef int long long ll;

stack< pair<ll,ll> > a1;
stack< pair<ll,ll> > a2;

ll dp[N];

ll n , t;

ll Pri[N];
ll Time[N];

void add(ll x){

  ll mn = a1.empty() ? x : min(x,a1.top().second);
  a1.push(make_pair(x,mn));

}

int mini(){

  ll mn;

  if( a1.empty() || a2.empty() ) mn = a1.empty() ? a2.top().second : a1.top().second;
  else mn = min( a1.top().second , a2.top().second );
  return mn;

}

void remove(){

  if(a2.empty()){

    while(!a1.empty()){

      ll ele = a1.top().first;
      a1.pop();
      ll mn = a2.empty() ? ele : min(ele,a2.top().second);
      a2.push(make_pair(ele,mn));

    }

  }

  a2.pop();

}

bool func(ll r , ll tempo , ll fim){

  memset(dp,0,sizeof(dp));
  for(int i = 1 ; i <= r ; i++) dp[i] = Time[i];

  for(int i = 0 ; i <= fim ; i++){

    if(a1.size() + a2.size() >= r + 1) remove();
    if(i > r) dp[i] = mini() + Time[i];
    add(dp[i]);

  }

  while(!a1.empty()) a1.pop();
  while(!a2.empty()) a2.pop();

  for(int i = 1 ; i <= fim ; i++) dp[i] += i;

  if(dp[fim] <= tempo) return true;
  else return false;

}

int bs(ll l , ll r , ll tempo){

  if(l == r) return l;

  ll mid = (l+r)/2;

  if(func(mid,tempo,n-1)) return bs(l,mid,tempo);

  else return bs(mid+1,r,tempo);

}

int main(){

  ifstream cin("journey.in");
  ofstream cout("journey.out");

  cin >> n >> t;

  for(int i = 1 ; i <= n - 1 ; i++) cin >> Pri[i];
  for(int i = 1 ; i <= n - 2 ; i++) cin >> Time[i];

  ll x = bs(1,n-1,t);
  ll mn = 100000000;

  for(int i = x ; i <= n - 1 ; i++) mn = min(mn,Pri[i]);

  cout << mn << "\n";

  return 0;

}