#include <bits/stdc++.h>
#include <experimental/random>
#include <random>
//#include <ext/pb_ds/assoc_container.hpp>
//using namespace __gnu_pbds;
using namespace std;
using ld = long double;
using ll = long long;
const ll INF = 3e18, MOD = 1e9 + 7;
void solve();
signed main() {
#ifdef LOCAL
freopen("input.txt", "r", stdin);
freopen("output.txt", "w", stdout);
#endif
ios::sync_with_stdio(false);
cin.tie(0);
int q = 1;
//cin >> q;
while (q--) {
solve();
}
}
void solve() {
ll n, m; cin >> n >> m;
vector<ll> a(n), b(n);
for (int i = 0; i < n; i++) cin >> a[i];
for (int i = 0; i < n; i++) cin >> b[i];
ll l = 0, r = INF;
while (r - l > 1) {
ll mid = (l + r) / 2;
ll all = 0;
for (int i = 0; i < n; i++) {
if (all > n * m) break;
if (b[i] >= a[i]) all += (mid + b[i] - 1) / b[i];
else {
ll x = min(m, (mid + a[i] - 1) / a[i]);
all += x; ll nado = max(0ll, mid - a[i] * x);
all += (nado + b[i] - 1) / b[i];
}
}
if (all <= n * m) l = mid;
else r = mid;
}
cout << l;
}
