#include <iostream>
#include <vector>
using namespace std;
int solve(long long target, int n, int m, vector<int> &classes, vector<int> &study) {
vector <long long> required(n);
for (int i = 0; i < n; i++) {
required[i] = target;
}
long long hours = 1LL * n * m; // how many hours of study i have left
// find out classes for which it's better to go to the courses
for (int i = 0; i < n; i++) {
if (classes[i] > study[i]) {
long long needed = required[i] / classes[i];
if (required[i] % classes[i] > 0) {
needed++;
}
if (needed > m) {
needed = m;
}
required[i] = max(0LL, required[i] - needed * classes[i]);
hours -= needed;
if (hours < 0) {
return 0;
}
}
}
// subtract comprehension value based on remaining time
for (int i = 0; i < n; i++) {
long long needed = required[i] / study[i];
if (required[i] % study[i] > 0) {
needed++;
}
hours -= needed;
if (hours < 0) {
return 0;
}
}
return 1;
}
int main() {
ios_base::sync_with_stdio(false);
cin.tie(NULL);
int n, m;
cin >> n >> m;
vector <int> classes(n), study(n);
for (int i = 0; i < n; i++) {
cin >> classes[i];
}
for (int i = 0; i < n; i++) {
cin >> study[i];
}
long long L = 0;
long long R = 1e18;
long long ans = 0;
while (L <= R) {
long long mid = (L + R) / 2;
if (solve(mid, n, m, classes, study)) {
ans = mid;
L = mid + 1;
}
else {
R = mid - 1;
}
}
cout << ans << '\n';
return 0;
}
