#include <bits/stdc++.h>
using namespace std;
#define int long long
#define INF (int)1e15
#define f first
#define s second
mt19937_64 RNG(chrono::steady_clock::now().time_since_epoch().count());
void Solve()
{
int n, m; cin >> n >> m;
vector <int> a(n), b(n);
for (auto &x : a) cin >> x;
for (auto &x : b) cin >> x;
int l = 0, r = INF;
while (r != l){
int mid = (l + r + 1) / 2;
int use = 0, need = 0;
for (int i = 0; i < n; i++){
if (a[i] < b[i]) {
need += (mid + b[i] - 1) / b[i];
if (use + need > n * m) break;
continue;
}
int o = (mid + a[i] - 1) / a[i];
int o1 = 0;
if (o > m){
o = m;
int ex = mid - a[i] * o;
o1 = (ex + b[i] - 1) / b[i];
assert(o1 >= 0);
}
int ex = a[i] * o + b[i] * o1 - mid;
int sw = ex / (a[i] - b[i]);
if (sw > o) sw = o;
o -= sw;
o1 += sw;
use += o;
need += o1;
if (use + need > n * m) break;
}
if (use + need > n * m) r = mid - 1;
else l = mid;
}
cout << l << "\n";
}
int32_t main()
{
auto begin = std::chrono::high_resolution_clock::now();
ios_base::sync_with_stdio(0);
cin.tie(0);
int t = 1;
// cin >> t;
for(int i = 1; i <= t; i++)
{
//cout << "Case #" << i << ": ";
Solve();
}
auto end = std::chrono::high_resolution_clock::now();
auto elapsed = std::chrono::duration_cast<std::chrono::nanoseconds>(end - begin);
cerr << "Time measured: " << elapsed.count() * 1e-9 << " seconds.\n";
return 0;
}
