/*
"TLE is like the wind, always by my side"
- Yasuo - 2022 -
*/
#include <bits/stdc++.h>
#define debug(x) cerr << #x << " " << x << "\n"
#define debugs(x) cerr << #x << " " << x << " "
#pragma GCC optimize("Ofast")
#define int long long
using namespace std;
int n,m,i,j,r,pas;
int a[300001];
int b[300001];
int courseneed(int val, int a, int b)
{
int ans;
ans=0;
if (a*m<val)
{
ans+=m;
val-=a*m;
if (val%b==0)
ans+=val/b;
else
ans+=val/b+1;
}
else
{
if (val%a==0)
ans+=val/a;
else
ans+=val/a+1;
}
return ans;
}
bool possible(int minimum)
{
int sum;
sum=0;
for (i=1;i<=n;i++)
{
sum+=courseneed(minimum,a[i],b[i]);
}
if (sum<=n*m)
return 1;
return 0;
}
signed main()
{
ios_base::sync_with_stdio(false);
cin.tie(0);
cout.tie(0);
cin >> n >> m;
for (i=1;i<=n;i++)
{
cin >> a[i];
}
for (i=1;i<=n;i++)
{
cin >> b[i];
}
for (i=1;i<=n;i++)
{
a[i]=max(a[i],b[i]);
}
r=0;
pas=(1<<30);
while (pas)
{
if (possible(r+pas))
r+=pas;
pas=pas/2;
}
cout << r;
}
