/*****from dust I have come, dust I will be*****/
#include<bits/stdc++.h>
#include<ext/pb_ds/assoc_container.hpp>
#include<ext/pb_ds/tree_policy.hpp>
using namespace __gnu_pbds;
using namespace std;
#define int long long
#define forn(i,n) for(int i=0;i<n;i++)
int dx[8] = { 1, 0, -1, 0, -1, 1, -1, 1 };
int dy[8] = { 0, 1, 0, -1, -1, 1, 1, -1 };
int ceil_div(int a, int b) {return a % b == 0 ? a / b : a / b + 1;}
const int MOD = 1000000007;
//const int MOD = 998244353;
typedef tree<int, null_type, less<int>, rb_tree_tag, tree_order_statistics_node_update> pbds; // find_by_order, order_of_key
/*
int k = A.order_of_key(p[i].second);
A.erase(A.find_by_order(k));
erase element from pbds multiset
*/
bool ok(vector<int>&a, int n, int v, int target){
forn(i,n){
int x = ceil_div(target, a[i]);
//cout <<x<<'\n';
v -= x;
if (v < 0) return false;
}
return (v >= 0);
}
int binary(vector<int>&a, int n, int v){
int l = 0, r = 5 * 1e18;
int ans = 0;
while (l <= r){
int mid = (l + r) / 2;
if (ok(a, n, v, mid)){
ans = mid;
l = mid + 1;
}
else r = mid - 1;
}
return ans;
}
bool ok2(vector<pair<pair<int, int>, pair<int, int>>>&skup, int target, int u, int m){
int tmp = target;
forn(i,(int)skup.size()){
target = tmp;
if (u < 0) return false;
auto v = skup[i];
//cout <<v.first.first<<' '<<v.first.second<<'\n';
if (v.first.first >= target) break;
if (v.second.second >= v.second.first){
int x = ceil_div(target, v.second.second);
v.first.first += (v.second.second * x);
u -= x;
}
else{
int y = m - v.first.second; //koliko mozemo
int potrebno = ceil_div(target, v.second.first); //koliko je potrebno
if (potrebno <= y){
v.first.second += potrebno;
v.first.first += (v.second.first * potrebno); //dodaj v
u -= potrebno;
}
else{
v.first.second = m;
target -= y * v.second.first;
v.first.first += y * v.second.first;
u -= y;
potrebno = ceil_div(target, v.second.second);
v.first.first += (v.second.second * potrebno);
u -= potrebno;
}
}
//cout <<v.first.first<<' '<<v.first.second<<' '<<v.second.first<<' '<<v.second.second<<'\n';
}
//cout <<u<<'\n';
return (u >= 0);
}
int binary2(vector<pair<pair<int, int>, pair<int, int>>>&skup, int n, int m){
int l = 0,r = 1e18;
int ans = 0;
while (l <= r){
int mid = (l + r) / 2;
if (ok2(skup, mid, n*m, m)){
ans = mid;
l = mid + 1;
}
else r= mid - 1;
}
return ans;
}
void solve(){
int n, m; cin >> n >> m;
vector<int>a(n); for (auto &t : a) cin >> t;
vector<int>b(n); for (auto &t : b) cin >> t;
if (a == b) cout << binary(a, n, n*m)<<'\n';
else{
vector<pair<pair<int, int>, pair<int, int>>>skup;
forn(i,n) skup.push_back({{0, 0}, {a[i], b[i]}});
sort(skup.begin(), skup.end());
cout <<binary2(skup,n,m)<<'\n';
}
}
int32_t main(){
ios_base::sync_with_stdio(0); cin.tie(0); cout.tie(0);
int t = 1; //cin >>t;
for (int i=1;i<=t;i++){
solve();
}
return 0;
}
