#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
const ll INF = 1e9+7;
const ll MOD = 998244353;
typedef pair<ll,ll> ii;
#define iii pair<ll,ii>
#define f(i,a,b) for(ll i = a;i < b;i++)
#define pb push_back
#define vll vector<ll>
#define F first
#define S second
#define all(x) (x).begin(), (x).end()
///I hope I will get uprating and don't make mistakes
///I will never stop programming
///sqrt(-1) Love C++
///Please don't hack me
///@TheofanisOrfanou Theo830
///Think different approaches (bs,dp,greedy,graphs,shortest paths,mst)
///Stay Calm
///Look for special cases
///Beware of overflow and array bounds
///Think the problem backwards
///Training
int main(){
ios_base::sync_with_stdio(0);
cin.tie(0);
ll l = 0,r = 1e18;
ll ans = 0;
ll n,m;
cin>>n>>m;
ll a[n],b[n];
f(i,0,n){
cin>>a[i];
}
f(i,0,n){
cin>>b[i];
}
while(l <= r){
ll mid = (l+r)/2;
ll A = 0,B = 0;
f(i,0,n){
if(b[i] >= a[i]){
B += (mid + b[i] - 1) / b[i];
}
else{
ll posa = min(m,(mid + a[i] - 1) / a[i]);
A += posa;
ll num = max(0LL,mid - posa * a[i]);
B += (num + b[i] - 1) / b[i];
}
if(A + B > n * m){
break;
}
}
if(A + B <= n*m){
l = mid + 1;
ans = max(ans,mid);
}
else{
r = mid - 1;
}
}
cout<<ans<<"\n";
}
