#include <bits/stdc++.h>
#define For(i,a,b) for(int i=a;i<=b;i++)
#define Forr(i,a,b) for(int i=a;i>=b;i--)
#define F first
#define S second
#define sz(x) ((int)x.size())
#define all(x) x.begin(),x.end()
#define eb emplace_back
#define INF (ll)(9e18)
#define int __int128_t
using namespace std;
using LL=long long;
using pii=pair<int,int>;
const int MAXN=300030;
int a[MAXN];
int b[MAXN];
bool check(__int128_t n,__int128_t m,__int128_t tar){
__int128_t s=0,d=0;
For(i,1,n){
if(m*a[i]>=tar){
s+=(m*a[i]-tar)/a[i];
}else{
int t=tar-m*a[i];
d+=(t+b[i]-1)/b[i];
}
}
return s>=d;
}
int32_t main(){
ios::sync_with_stdio(false);
cin.tie(0);
// OAO
long long n,m; cin>>n>>m;
For(i,1,n){
long long t; cin>>t;
a[i]=t;
}
For(i,1,n){
long long t; cin>>t;
b[i]=t;
a[i]=max(a[i],b[i]);
}
int hi=1e18+10;
int lo=0;
while(hi-lo>1){
int mi=(hi+lo)/2;
if(check(n,m,mi)) lo=mi;
else hi=mi;
}
cout<<(long long)lo<<"\n";
return 0;
}
