#include <bits/stdc++.h>
using namespace std;
#define sz(v) int(v.size())
#define ar array
typedef long long ll;
const int MAXN = 2e5+10, MOD = 1e9+7;
const ll INF = (long long)1e18+10;
void solve() {
// a[i] := max(a[i], b[i])
// binary search, take the minimum number of a's such that I'm satisfied
int n; ll m; cin >> n >> m;
vector<ll> a(n), b(n);
for (auto& x : a) cin >> x;
for (auto& x : b) cin >> x;
for (int i = 0; i < n; i++) a[i] = max(a[i], b[i]);
auto v = [&](ll x) -> bool {
__int128 has = 0;
for (int i = 0; i < n; i++) {
ll need = (x + a[i] - 1) / a[i];
if (need <= m) has += m - need;
else has -= (x - a[i] * m + b[i] - 1) / b[i];
}
return has >= 0;
};
ll lo = 0, hi = INF, mid = (lo + hi) / 2;
while (lo < mid && mid < hi) {
if (v(mid)) lo = mid;
else hi = mid;
mid = (lo + hi) / 2;
}
cout << lo << '\n';
}
int main() {
ios::sync_with_stdio(false); cin.tie(0);
int T=1;
// cin >> T;
while (T--) solve();
}
