// #pragma GCC optimize("O3")
// #pragma GCC optimization("Ofast,unroll-loops")
// #pragma GCC target("avx2,bmi,bmi2,lzcnt,popcnt")
#include <bits/stdc++.h>
using namespace std;
#define int long long
#define ll long long
#define FOR(i, l, r) for (int i = (l); i <= (r); i++)
#define FOD(i, r, l) for (int i = (r); i >= (l); i--)
#define fi first
#define se second
#define pii pair<int, int>
const ll mod = 1e9 + 7;
const int MAXN = 3e5 + 5;
const ll oo = 1e18 + 7;
const int base = 10;
int n, m;
int a[MAXN], b[MAXN];
vector<pii> vec;
bool check(int mid){
int du=0;
for(auto [x, id]:vec){
// cout << x << ' ' << id << '\n';
if(x>=mid){
int thua=x-mid;
du+=thua/max(a[id], b[id]);
// cout << du << ' ';
}
else{
int thieu=mid-x;
du-=(thieu+b[id]-1)/b[id];
}
}
if(du < 0)return 0;
return 1;
}
signed main()
{
ios_base::sync_with_stdio(false);
cin.tie(NULL);
// freopen("test.txt", "r", stdin);
// freopen("o2.out", "w", stdout);
if(fopen(".inp", "r")){
freopen(".inp", "r", stdin);
freopen(".out", "w", stdout);
}
cin >> n >> m;
FOR(i, 1, n){
cin >> a[i];
}
FOR(i, 1, n){
cin >> b[i];
}
FOR(i, 1, n){
vec.push_back({max(a[i], b[i])*m, i});
}
int l=0, r=1e18, ans=0;
while(l<=r){
int mid=(l+r)/2;
if(check(mid)){
ans=mid;
l=mid+1;
}
else{
r=mid-1;
}
}
cout << ans;
return 0;
}
