#ifdef __AVX2__
#pragma GCC target "avx2"
#endif
#pragma GCC optimize "O3"
#pragma GCC optimize "unroll-loops"
#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 elif else if
#define all(l) begin(l),end(l)
#define rall(l) rbegin(l),rend(l)
#define append push_back
#define print(l) for(auto i:l) cout<<i<<' '; cout<<endl;
#define pprint(a,b) cout<<a<<' '<<b<<endl;
#define inp(l) for(auto &i:l) cin>>i;
#define ordered_set tree<int, null_type,less<int>, rb_tree_tag,tree_order_statistics_node_update>
#define pai make_pair
#define endl "\n"
#define pii pair<int,int>
#define fi first
#define se second
#define vec vector
// const int mod=998244353;
const int mod1=998244353;
const int mod=1e9+7;
const int N=2e5+5;
int iter=1,itera=1;
void solve(){
int n,d;
cin>>n>>d;
vec<int>a(n),b(n);
inp(a);
inp(b);
for(int i=0;i<n;i++) a[i]=max(a[i],b[i]);
int l=0,r=1e18;
r+=2;
int k=1e10;
while(l+1<r){
int m=(l+r)/2;
int ne=0,ex=0;
int ne1=0,ex1=0;
for(int i=0;i<n;i++){
int g=a[i]*d;
if(g>=m){
g-=m;
ex+=g/a[i];
ex1+=ex/k;
ex%=k;
}
else{
g=m-g;
ne+=(g+b[i]-1)/b[i];
ne1+=ne/k;
ne%=k;
}
}
if(ex1>ne1 or (ex1==ne1 and ex>=ne)) l=m;
else r=m;
}
cout<<l<<endl;
// cout<<log(l)/log(10)<<endl;
}
signed main(){
// freopen("","r",stdin);
// freopen("","w",stdout);
ios_base::sync_with_stdio(false);
cin.tie(NULL);
cout.tie(NULL);
cout<<fixed<<setprecision(20);
// cin>>itera;
for(iter=1;iter<=itera;iter++) solve();
}
