#include <bits/stdc++.h>
#pragma GCC optimize("O3")
#pragma GCC optimize("unroll-loops")
#define ll long long
#define endl '\n'
#define pb push_back
#define fi first
#define se second
#define pii pair<int, int>
using namespace std;
ll mas[300001], mas2[300001];
bool var(ll x, ll n, ll m)
{
ll vaj=0, ir=n*m;
for(int i=1; i<=n; i++)
{
if(mas[i]>mas2[i])
{
ll v1=(x+mas[i]-1)/mas[i];
v1=min(m, v1);
ir-=v1;
ll p=max(0ll, x-mas[i]*v1);
vaj+=(mas2[i]+p-1)/mas2[i];
}
else
vaj+=(x+mas2[i]-1)/mas2[i];
if(vaj>n*m)
return 0;
}
return (ir>=vaj);
}
int main()
{
ios_base::sync_with_stdio(0);
cin.tie(0);
ll n, m;
cin >> n >> m;
for(ll i=1; i<=n; i++)
cin >> mas[i];
for(ll i=1; i<=n; i++)
cin >> mas2[i];
ll l=1, r=1e18;
while(l<r)
{
ll mid=(l+r+1)/2;
if(var(mid, n, m))
l=mid;
else
r=mid-1;
}
cout << l << endl;
return 0;
}
