#include<bits/stdc++.h>
using namespace std;
const int MAXN=3e5+5;
long long A[MAXN],B[MAXN];
int main()
{
ios::sync_with_stdio(0);
cin.tie(0);
cout.tie(0);
long long n,k;
cin>>n>>k;
for(int i=1;i<=n;i++) cin>>A[i];
for(int i=1;i<=n;i++) cin>>B[i];
long long l=1,r=1e18,ans=0;
while(l<=r)
{
long long mid=(l+r)/2,sum=0,s=n*k;
for(int i=1;i<=n&&sum<=s;i++) if(A[i]>B[i])
{
long long t=min(k,(mid+A[i]-1)/A[i]);
s-=t,sum+=(max(0LL,mid-t*A[i])+B[i]-1)/B[i];
}
else sum+=(mid+B[i]-1)/B[i];
if(sum<=s) l=mid+1,ans=mid;
else r=mid-1;
}
cout<<ans;
}
