#include <bits/stdc++.h>
using namespace std;
#define int long long
const int inf=1e18;
signed main()
{
int n,m;cin>>n>>m;
int a[n+1],b[n+1];
for(int i=1;i<=n;i++)cin>>a[i];
for(int i=1;i<=n;i++)cin>>b[i];
int l=1,r=inf,mid=l+(r-l)/2,res=0;
while(l<=r)
{
//printf("%lld %lld %lld: ",l,mid,r);
int sum=0;
for(int i=1;i<=n;i++)
{
int x,z,k=inf;
if(a[i]<=b[i])
{
x=0;
z=(mid-x*(a[i]-b[i])+b[i]-1)/b[i];
k=max(x,z);
}
else
{
x=mid/a[i];
if(x>m) x=m;
z=(mid-x*(a[i]-b[i])+b[i]-1)/b[i];
k=min(k,max(x,z));
x++;
if(x>m) x=m;
z=(mid-x*(a[i]-b[i])+b[i]-1)/b[i];
k=min(k,max(x,z));
}
sum+=k;
/*int k1=inf;
for(int j=0;j<=m;j++)
{
int z=ceil((double)(mid-j*(a[i]-b[i]))/b[i]);
k1=min(k1,max(j,z));
}*/
/*int x=0;
if(a[i]>b[i])x=min(mid/(a[i]-b[i]),m);
sum+=ceil((mid-x*(a[i]-b[i]))/b[i]);*/
//cout<<"|"<<k<<" "<<k1<<"| ";
}
//cout<<endl;
if(sum<=n*m)
{
res=mid;
l=mid+1;
}
else r=mid-1;
mid=l+(r-l)/2;
}
cout<<res<<endl;
return 0;
}
