#include<bits/stdc++.h>
using namespace std;
#define fast ios_base::sync_with_stdio(0);cin.tie(0);cout.tie(0);
#define in insert
#define all(x) x.begin(),x.end()
#define pb push_back
#define eb emplace_back
#define ff first
#define ss second
#define int long long
typedef long long ll;
typedef vector<int> vi;
typedef set<int> si;
typedef multiset<int> msi;
typedef pair<int, int> pii;
typedef vector<pii> vpii;
// typedef pair<int, int> P;
template<typename T, typename U>
ostream & operator << (ostream &out, const pair<T, U> &c) {
out << c.first << ' ' << c.second;
return out;
}
template<typename T>
ostream & operator << (ostream &out, vector<T> &v) {
const int sz = v.size();
for (int i = 0; i < sz; i++) {
if (i) out << ' ';
out << v[i];
}
return out;
}
template<typename T>
istream & operator >> (istream &in, vector<T> &v) {
for (T &x : v) in >> x;
return in;
}
template<typename T, typename U>
istream & operator >> (istream &in, pair<T, U> &c) {
in >> c.first;
in >> c.second;
return in;
}
template<typename T>
void mxx(T &a, T b){if(b > a) a = b;}
template<typename T>
void mnn(T &a, T b){if(b < a) a = b;}
const int mxn = 3e5 + 10, MXLOG = 22, mod = 1e9 + 7, P = 1181, D = 1523;
const long long inf = 2e18 + 10;
int a[mxn], b[mxn], x[mxn], n, m;
bool check(int mid) {
int mn = 0, mx = 0;
for(int i = 1; i <= n; i++) {
if(x[i] < mid) mn += (mid - x[i] + b[i] - 1) / b[i];
if(x[i] > mid) mx += (x[i] - mid) / a[i];
mnn(mn, inf);
mnn(mx, inf);
}
return mn <= mx;
}
void go() {
cin >> n >> m;
for(int i = 1; i <= n; i++) {
cin >> a[i];
}
for(int i = 1; i <= n; i++) {
cin >> b[i];
}
int l = 1e18 + 10, r = 1e18 + 10;
for(int i = 1; i <= n; i++) {
mxx(a[i], b[i]);
x[i] = a[i] * m;
mnn(l, x[i]);
}
while(r - l > 1) {
int mid = (l + r) / 2;
if(check(mid)) l = mid;
else r = mid;
}
cout << l << '\n';
}
signed main() {
fast;
int t = 1;
// cin >> t;
while(t--) {
go();
}
return 0;
}
