#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
typedef long double ld;
typedef pair<ll,ll> pl;
typedef pair<int,int> pii;
typedef tuple<int,int,int> tt;
#define all(a) a.begin(), a.end()
#define filter(a) a.erase(unique(all(a)), a.end())
const int mn = 3e5 + 5;
ll a[mn], b[mn], cur[mn];
ll n, m;
bool ok (ll lb) {
ll period = n * m;
for (int i = 0; i < n; i++) {
cur[i] = 0;
if (a[i] < b[i]) continue;
ll need = min(m, lb / a[i] + (lb % a[i] ? 1 : 0));
cur[i] = need * a[i], period -= need;
}
for (int i = 0; i < n; i++) {
if (cur[i] >= lb) continue;
ll need = (lb - cur[i]) / b[i] + ((lb - cur[i]) % b[i] ? 1 : 0);
if (need > period) return 0;
period -= need;
}
return 1;
}
int main()
{
ios::sync_with_stdio(0);
cin.tie(0);
cin >> n >> m;
for (int i = 0; i < n; i++) cin >> a[i];
for (int i = 0; i < n; i++) cin >> b[i];
ll ans = 0;
for (ll i = (1LL << 59); i; i >>= 1)
if (ok((ans | i))) ans |= i;
cout << ans;
return 0;
}
