#include <bits/stdc++.h>
#define ll long long
#define ar array
#define db double
#define all(x) x.begin(), x.end()
#define sz(x) (int)x.size()
using namespace std;
mt19937 rng(chrono::steady_clock::now().time_since_epoch().count());
#define rint(l, r) uniform_int_distribution<int>(l, r)(rng)
template<typename T> bool ckmin(T &a, const T &b) { return a > b ? a = b, 1 : 0; }
template<typename T> bool ckmax(T &a, const T &b) { return a < b ? a = b, 1 : 0; }
void test_case() {
int n, m;
cin >> n >> m;
vector<int> a(n), b(n);
for (int &x : a) cin >> x;
for (int &x : b) cin >> x;
ll l = 1, r = 1e18, ans = 1;
while (l <= r) {
ll mid = (l+r)/2, used = 0;
for (int i = 0; i < n; i++) {
ll cur = mid;
if (a[i] > b[i]) {
ll use = min<ll>(m, (cur + a[i] - 1) / a[i]);
cur -= use * a[i];
used += use;
}
if (cur > 0) used += (cur + b[i] - 1) / b[i];
if (used > (ll)n*m) break;
}
if (used <= (ll)n*m) ans = mid, l = mid+1;
else r = mid-1;
}
cout << ans << '\n';
}
int main() {
cin.tie(0)->sync_with_stdio(0);
int t = 1;
// cin >> t;
while (t--) test_case();
}
