#include <bits/stdc++.h>
#define endl "\n"
using namespace std;
namespace std {
template <int D, typename T>
struct Vec : public vector<Vec<D - 1, T>> {
static_assert(D >= 1);
template <typename... Args>
Vec(int n = 0, Args... args) : vector<Vec<D - 1, T>>(n, Vec<D - 1, T>(args...)) {}
};
template <typename T>
struct Vec<1, T> : public vector<T> {
Vec(int n = 0, T val = T()) : std::vector<T>(n, val) {}
};
template <class Fun>
class y_combinator_result {
Fun fun_;
public:
template <class T>
explicit y_combinator_result(T &&fun) : fun_(std::forward<T>(fun)) {}
template <class... Args>
decltype(auto) operator()(Args &&...args) {
return fun_(std::ref(*this), std::forward<Args>(args)...);
}
};
template <class Fun>
decltype(auto) y_combinator(Fun &&fun) {
return y_combinator_result<std::decay_t<Fun>>(std::forward<Fun>(fun));
}
} // namespace std
#define int long long
void solve() {
int n, m; cin >> n >> m;
vector<int> a(n), b(n);
for (int i = 0; i < n; i++) cin >> a[i];
for (int i = 0; i < n; i++) cin >> b[i];
for (int i = 0; i < n; i++) {
a[i] = max(a[i], b[i]);
}
long long l = 0, r = 1e18, ans = -1;
while (l <= r) {
long long mid = l + r >> 1;
long long cur = 0;
for (int i = 0; i < n; i++) {
long long tmp = 1LL * a[i] * m;
if (tmp >= mid) {
cur += (tmp - mid) / a[i];
} else {
cur -= (mid - tmp + b[i] - 1) / b[i];
}
cur = max(cur, (long long) -1e18);
}
if (cur >= 0) {
ans = mid;
l = mid + 1;
} else r = mid - 1;
}
assert(ans != -1);
cout << ans;
}
int32_t main() {
ios_base::sync_with_stdio(0);
cin.tie(0);
int t = 1;
// cin >> t;
while (t--) {
solve();
}
}
