#include<bits/stdc++.h>
using namespace std;
#define ll long long
const bool Multitest = 0;
const int N = 3e5 + 10;
ll a[N], b[N]; int n, m;
bool check(ll a, ll b, ll c)
{
if((int) log2(a) + (int) log2(b) > log2(c)) return 1;
return 0;
}
bool check(ll val)
{
ll cnt = 0;
for(int i = 1 ; i <= n ; i++)
{
if(a[i] < b[i])
{
if(b[i] * m < val) return 0;
int l = 0, r = m, pos = -1;
while(l <= r)
{
int mid = (l + r) >> 1;
if(a[i] * mid + b[i] * (m - mid) >= val) l = mid + 1, pos = mid;
else r = mid - 1;
}
if(pos == -1) return 0;
cnt += pos;
// cout << i << ' ' << pos << '\n';
}
}
for(int i = 1 ; i <= n ; i++)
{
if(a[i] < b[i]) continue;
if(a[i] * m >= val)
{
int l = 1, r = m, pos = 0;
while(l <= r)
{
int mid = (l + r) >> 1;
if(a[i] * mid >= val) r = mid - 1, pos = mid;
else l = mid + 1;
}
pos = m - pos;
// cout << i << ' ' << pos << '\n';
cnt += pos;
}
else
{
ll l = 0, r = n * m, pos = -1;
while(l <= r)
{
ll mid = (l + r) >> 1;
if(check(a[i], m, val) || check(b[i], mid, val))
{
r = mid - 1, pos = mid;
continue;
}
if(a[i] * m + b[i] * mid >= val) r = mid - 1, pos = mid;
else l = mid + 1;
}
if(pos == -1) return 0;
// cout << i << ' ' << pos << ' ' << cnt << '\n';
cnt -= pos;
}
}
return cnt >= 0;
}
void work()
{
cin >> n >> m;
for(int i = 1 ; i <= n ; i++) cin >> a[i];
for(int i = 1 ; i <= n ; i++) cin >> b[i];
ll l = 1, r = 1e18, pos = -1;
//
// cout << check(7) << '\n';
//
// return;
while(l <= r)
{
ll mid = (l + r) >> 1;
if(check(mid)) l = mid + 1, pos = mid;
else r = mid - 1;
}
cout << pos;
}
int main()
{
ios_base::sync_with_stdio(false);
cin.tie(0); cout.tie(0);
int q = 1;
if(Multitest) cin >> q;
while(q--) work();
}
