#ifdef LOCAL
//#define _GLIBCXX_DEBUG
#endif
#include <bits/stdc++.h>
#include <random>
#ifndef LOCAL
//#pragma GCC optimize("O3")
//#pragma GCC optimize("Ofast")
//#pragma GCC optimize("unroll-loops")
#pragma GCC target("avx,avx2,bmi,bmi2,popcnt,lzcnt")
#endif
using namespace std;
using ll = long long;
using ld = long double;
#define x first
#define y second
#define all(x) x.begin(), x.end()
#define rall(x) x.rbegin(), x.rend()
mt19937_64 mt(418);
void solve();
void init();
int32_t main() {
#ifndef LOCAL
cin.tie(nullptr)->sync_with_stdio(false);
#else
freopen("input.txt", "r", stdin);
#endif
// srand(time(0));
init();
cout << fixed << setprecision(20);
int t = 1;
// cin >> t;
while (t--) {
solve();
}
}
void init() {}
#define int ll
void solve() {
int n, m;
cin >> n >> m;
vector<int> a(n), b(n);
for (int i = 0; i < n; i++) {
cin >> a[i];
}
for (int i = 0; i < n; i++) {
cin >> b[i];
}
ll l = 0, r = 2e18;
while (r - l > 1) {
ll mid = (r + l) / 2;
ll free = (ll)m * n;
vector<ll> skill(n, 0);
int ok = 1;
for (int i = 0; i < n; i++) {
if (a[i] > b[i]) {
ll have = (mid + a[i] - 1) / a[i];
have = min(have, (ll)m);
skill[i] += a[i] * have;
free -= have;
}
}
for (int i = 0; i < n; i++) {
if (free < 0) {
ok = 0;
}
ll need = mid - skill[i];
if (need > 0) {
ll have = (need + b[i] - 1) / b[i];
skill[i] += b[i] * have;
free -= have;
}
}
if (free >= 0 && ok) {
l = mid;
} else {
r = mid;
}
// cout << "!!! " << r << ' ' << l << '\n';
}
cout << l << '\n';
}
