#include<bits/stdc++.h>
typedef long long ll;
#define pb push_back
#define fr first
#define sc second
using namespace std;
int n,m;
ll a[300023],b[300023];
bool f(ll x){
ll ek=0;
for(int i=1;i<=n;i++){
if(m*a[i]==x)continue;
if(m*a[i]>x){
ek+=m-((x-1)/a[i]+1);
}
else{
ek-=(x-m*a[i]-1)/b[i]+1;
}
}
return ek>=0;
}
int main(){
ios_base::sync_with_stdio(false);cin.tie(NULL);
cin>>n>>m;
for(int i=1;i<=n;i++){
cin>>a[i];
}
for(int i=1;i<=n;i++){
cin>>b[i];
a[i]=max(a[i],b[i]);
}
ll l=1,r=1000000000000000000ll;
while(l<r){
ll mi=(l+r+1)>>1;
if(f(mi))l=mi;
else r=mi-1;
}
cout<<max(min(max(min(l,r),min(l,r)),max(min(l,r),min(l,r))),min(max(min(l,r),min(l,r)),max(min(l,r),min(l,r))));
}
