#include <bits/stdc++.h>
using namespace std;
#define int long long
mt19937_64 RNG(chrono::steady_clock::now().time_since_epoch().count());
int n, m;
vector<int> a, b;
bool Check(int value) {
int temp = 0;
for(int i = 1; i <= n; i++) {
int credits = a[i] * m;
if(credits >= value) {
temp += (credits - value) / a[i]; //free courses you can take
}
else {
temp -= (value - credits + b[i] - 1) / b[i]; //number of courses you need to take
}
}
if(temp >= 0)
return true;
return false;
}
void Solve() {
cin >> n >> m;
a.resize(n + 1);
b.resize(n + 1);
for(int i = 1; i <= n; i++) {
cin >> a[i];
}
for(int i = 1; i <= n; i++) {
cin >> b[i];
}
for(int i = 1; i <= n; i++) {
a[i] = max(a[i], b[i]);
}
int l = 0, r = 1e18;
int ans = 0;
while(l <= r) {
int mid = (l + r) >> 1;
if(Check(mid)) {
ans = mid;
l = mid + 1;
}
else {
r = mid - 1;
}
}
cout << ans << "\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;
while(t--) {
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;
}
