#include <bits/stdc++.h>
using namespace std;
#define ll long long
#define pll pair<ll, ll>
#define pii pair<int, int>
#define fs first
#define sc second
#define pb push_back
void solve() {
ll n,m;
cin>>n>>m;
ll a[n],b[n];
for(int i=0;i<n;i++)cin>>a[i];
for(int i=0;i<n;i++){
cin>>b[i];
a[i]=max(a[i],b[i]);
}
ll inf=1e18;
ll l=0,r=inf;
while(l<r){
ll x=l+r+1>>1;
ll s1=0,s2=0;
for(int i=0;i<n;i++){
if(a[i]*m>=x){
s1+=m-(x+a[i]-1)/a[i];
}else{
s2=min(inf,s2+(x-a[i]*m+b[i]-1)/b[i]);
}
}
if(s1>=s2)l=x;
else r=x-1;
}
cout<<l<<'\n';
}
int main() {
ios_base::sync_with_stdio(0);cin.tie(0);cout.tie(0);
solve();
}
