#include <bits/stdc++.h>
#define ll __int128_t
#define int long long
#define IO ios::sync_with_stdio(0), cin.tie(0)
#define FOR(i, a, b) for (int i = a; i <= b; i++)
using namespace std;
using pii = pair<int, int>;
const int N = 300005;
const int INF = 2e18;
int n, m;
int a[N], b[N];
bool check(ll k) {
ll cst_day = 0;
for (int i = 1; i <= n; i++) {
if (a[i] >= b[i]) {
ll need = (k + a[i] - 1) / a[i];
if (need > m) {
ll less = k - m * a[i];
cst_day += (less + b[i] - 1) / b[i];
} else {
cst_day -= m - need;
}
} else {
ll need = (k + b[i] - 1) / b[i];
if (need > m)
cst_day += need - m;
else
cst_day -= m - need;
}
}
return (cst_day <= 0);
}
signed main() {
IO;
cin >> n >> m;
FOR(i, 1, n) cin >> a[i];
FOR(i, 1, n) cin >> b[i];
ll l = 0, r = 10000;
while (check(r))
r *= 2;
while (l + 1 < r) {
int mid = (l + r) >> 1;
if (check(mid))
l = mid;
else
r = mid;
}
int ans = l;
cout << ans << "\n";
return 0;
}
