#include <bits/stdc++.h>
using namespace std;
using ll = long long;
const int N = 3e5 + 24;
const ll INF = 1e18;
ll n, m, a[N], b[N];
void solve() {
cin >> n >> m;
for (int i = 1; i <= n; i++) {
cin >> a[i];
}
for (int i = 1; i <= n; i++) {
cin >> b[i];
}
ll res = INF;
for (ll l = 1, r = INF; l <= r; ) {
ll mid = (l + r) / 2;
ll s = 0; bool flag = 0;
for (int i = 1; i <= n; i++) {
if (a[i] * m >= mid) {
if (b[i] >= a[i]) {
ll add = m - (mid + b[i] - 1) / b[i];
s += add;
}
else {
ll add = m - (mid + a[i] - 1) / a[i];
s += add;
}
}
else if (b[i] * m >= mid) {
ll add = m - (mid + b[i] - 1) / b[i];
s += add;
}
}
for (int i = 1; i <= n; i++) {
if (a[i] * m < mid) {
if (b[i] * m >= mid) continue;
ll need = (mid - max(b[i], a[i]) * m + b[i] - 1) / (b[i]);
if (s < need) { flag = 1; break; }
s -= need;
}
}
if (!flag) res = mid, l = mid + 1;
else r = mid - 1;
}
cout << res << '\n';
}
int main() {
cin.tie(0) -> sync_with_stdio(0);
int T = 1; // cin >> T;
while (T--) {
solve();
}
}
