#include <bits/stdc++.h>
#include <climits>
using namespace std;
typedef long long ll;
bool works(ll mid, vector<ll> classes, vector<ll> selfstudy, ll n, ll m){
ll time = n*m;
for(ll i = 0; i<ll(classes.size()); i++){
ll need = mid;
if(classes[i] > selfstudy[i]){
//classes are more productive
ll classhours = need/classes[i];
if(need%classes[i] != 0){
classhours++;
}
classhours = min(classhours, m);
need = max(0ll, need-(classhours*classes[i]));
time-=classhours;
if(need>0){
ll selfstudyhours = need/selfstudy[i];
if(need%selfstudy[i] != 0){
selfstudyhours++;
}
time-=selfstudyhours;
}
}
else{
//selfstudy is more productive
ll selfstudyhours = mid/selfstudy[i];
if(mid%selfstudy[i] != 0){
selfstudyhours++;
}
time-=selfstudyhours;
}
if(time < 0) return false;
}
return time>=0;
}
int main() {
ll n, m;
cin >> n >> m;
vector<ll> classes(n), selfstudy(n);
for (int i = 0; i < n; i++) {
cin >> classes[i];
}
for (int i = 0; i < n; i++) {
cin >> selfstudy[i];
}
ll lo = 0, hi = ll(1e18), best = 0;
while (lo <= hi) {
ll mid = (lo+hi)/2;
if (works(mid, classes, selfstudy, n, m)) {
best = mid;
lo = mid + 1;
} else {
hi = mid - 1;
}
}
cout << best << endl;
return 0;
}
