#include <bits/stdc++.h>
using namespace std;
#define int long long
#define FOR(i,a,b) for (int i = (a); i < (b); ++i)
#define pb push_back
#define all(a) a.begin(), a.end()
#define endl "\n"
void printVector(vector<int> a){
for (auto x: a) cout << x << " ";
cout << endl;
}
void solve(){
int n, m; cin >> n >> m;
vector<int> a(n);
FOR(i,0,n) cin >> a[i];
vector<int> b(n);
FOR(i,0,n) cin >> b[i];
int l = 0; int r = 1e18;
int ans = 0;
int c = 0;
while (l <= r){
if (l == r) c++;
if (c > 2) break;
int mid = (l+r)/2ll;
int tot = 0ll;
bool can = true;
FOR(i,0,n){
int curr = 0;
if (a[i] > b[i]){
if (m*a[i] < mid){
int u = mid-m*a[i];
curr += m;
curr += (u+b[i]-1)/b[i];
}else{
curr += (mid+a[i]-1)/a[i];
}
}else{
curr += (mid+b[i]-1)/b[i];
}
tot += curr;
if (tot > n*m){
can = false;
break;
}
}
if (tot <= n*m && can){
ans = max(ans, mid);
if (l+1ll == r){
l = r;
}else{
l = mid;
}
}else{
if (l+1 == r){
ans = l;
break;
}
r = mid;
}
}
cout << ans << endl;
}
int32_t main(){
ios::sync_with_stdio(false);cin.tie(nullptr);
int t = 1; // cin >> t;
while (t--) solve();
}
