#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
const int MAXN = 3e5;
const ll INF = 1e18;
ll a[MAXN], b[MAXN];
int main() {
ios_base::sync_with_stdio(false); cin.tie(NULL);
int n; ll days; cin >> n >> days;
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; ll ans = 0;
while (l <= r) {
ll mid = (l + r) / 2;
ll available = 0, needed = 0;
for (int i=0; i<n; i++) {
ll val = max(a[i], b[i]);
ll need = (mid + val - 1) / val;
if (need <= days) available += days - need;
else needed += (mid - days * val + b[i] - 1) / b[i];
if (needed > n * days) break;
}
if (available >= needed) {
ans = mid;
l = mid+1;
} else r = mid-1;
}
cout << ans << '\n';
return 0;
}
