//#define _GLIBCXX_DEBUG
#include <bits/stdc++.h>
#define int long long
using namespace std;
const int INF = 1e18;
const int mod = 1e9+7;
bool check(vector <int> &A,vector <int> &B,int mid,int m) {
int balance = 0;
for (int i = 0; i < A.size(); i++) {
int need_time = (mid + A[i] - 1) / A[i];
if (need_time > 1)return 0;
if (m >= need_time) {
balance += (m - need_time);
}else {
int ost = mid - A[i] * m;
if (ost < 0)abort();
balance -= (ost + B[i] - 1) / B[i];
}
}
return balance >= 0;
}
signed main() {
ios_base::sync_with_stdio(false);
cin.tie(NULL);
int n,m;
cin >> n >> m;
vector <int> A(n),B(n);
for (int i = 0;i < n;i++) {
cin >> A[i];
}
int res = INF;
for (int i = 0;i < n;i++) {
cin >> B[i];
A[i] = max(A[i],B[i]);
res = min(res,A[i]);
}
int l = 0,r = 1e18 + 1;
while (r-l>1) {
int mid = l + (r-l)/2;
if (check(A,B,mid,m)) {
l = mid;
}else {
r = mid;
}
}
if (res > l)abort();
cout << l << "\n";
}
