//Dedicated to my love, ivaziva
#include <bits/stdc++.h>
using namespace std;
#define ll long long
#define pb push_back
#define pii pair<int,int>
#define all(x) x.begin(), x.end()
#define rall(x) x.rbegin(), x.rend()
#define sz(a) ((int)a.size())
const int N=3e5+5;
ll n, m;
ll a[N], b[N];
vector<pair<ll, pair<ll, ll>>> v;
bool check(ll mid) {
ll o=0;
for (auto x:v) {
ll mx=x.first, A=x.second.first, B=x.second.second;
if (A>=B) {
ll tr=min((mid+mx-1)/mx, m);
if (tr*mx>=mid) {
o+=(m-tr);
}
else {
ll tr2=(mid-min((mid+mx-1)/mx, m)*mx+B-1)/B;
if (tr2>o)
return false;
else
o-=tr2;
}
}
else {
ll tr=min((mid+mx-1)/mx, o);
if (tr*mx>=mid) {
o+=m;
}
else {
ll tr2=(mid-min((mid+mx-1)/mx, o)*mx+mx-1)/mx;
if (tr2>m)
return false;
else
o=m-tr2;
}
}
}
return true;
}
int main () {
ios::sync_with_stdio(false), cin.tie(0);
cin >> n >> m;
for (ll i=1; i<=n; i++)
cin >> a[i];
for (ll i=1; i<=n; i++)
cin >> b[i];
for (ll i=1; i<=n; i++) {
v.pb(make_pair(max(a[i], b[i]), make_pair(a[i], b[i])));
}
sort(rall(v));
ll lo=1, hi=(ll)(1e18), ans=0;
while (lo<=hi) {
ll mid=(lo+hi)/2;
if (check(mid)) {
lo=mid+1;
ans=mid;
}
else {
hi=mid-1;
}
}
cout << ans << '\n';
}
