#include <bits/stdc++.h>
#define all(x) x.begin(), x.end()
#define rall(x) x.rbegin(), x.rend()
//#define int long long
using namespace std;
using ll = long long;
using pii = pair<int, int>;
using pll = pair<ll, ll>;
const int mod = 1e9 + 7;
const int LOG = 20;
const int maxn = 1e5 + 5;
signed main() {
ll n, m;
cin >> n >> m;
vector<ll> a(n+1), b(n+1);
for(int i=1; i<=n; i++) cin >> a[i];
for(int i=1; i<=n; i++) cin >> b[i];
if(m == 1) {
ll ans = 1e18;
for(int i=1; i<=n; i++) ans = min(ans, max(a[i], b[i]));
cout << ans << '\n';
return 0;
}
__int128_t l=1, r=1e18, ans=0;
while(l <= r) {
__int128_t mid = (l + r) / 2;
__int128_t total = 0;
for(__int128_t i=1; i<=n; i++) total += (mid + a[i] - 1) / a[i];
if(total <= n * m) ans = mid, l = mid + 1;
else r = mid - 1;
}
cout << (ll)ans << '\n';
return 0;
}
