#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
typedef double db;
#define all(x) (x).begin(), (x).end()
#define md ((tl + tr) >> 1)
#define TL v + v, tl, md
#define TR v + v + 1, md + 1, tr
#define F first
#define S second
#define pii pair<int, int>
#define int ll
const int maxn = 5e5 + 7;
const ll inf = 2e18 + 7;
const double PI = atan2(0.0, -1.0);
int n, m, a[maxn], b[maxn], s[maxn];
bool check(int x) {
int cnt = 0;
for (int i = 1; i <= n && cnt >= -n * m; i++) {
if (s[i] >= x)
cnt += (s[i] - x) / a[i];
else
cnt -= (x - s[i] + b[i] - 1) / b[i];
}
return cnt >= 0;
}
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];
for (int i = 1; i <= n; i++) {
a[i] = max(a[i], b[i]);
s[i] = a[i] * m;
}
int l = 0, r = inf;
while (l + 1 < r) {
int mid = ((l + r) >> 1);
if (check(mid))
l = mid;
else
r = mid;
}
cout << l;
}
signed main() {
ios_base::sync_with_stdio(false);
cin.tie(0);
int test = 1;
// cin >> test;
while (test--) {
solve();
// cout << '\n';
}
return 0;
}
