#include <bits/stdc++.h>
using namespace std;
#define pi pair<int, int>
#define vi vector<int>
#define int unsigned long long
int ceil(int a, int b) {
return (a + b - 1) / b;
}
bool is_possible(int x, const vector<int>& a, const vector<int>& b, const vector<int>& enum_order, int m) {
int extra = 0;
for (int i : enum_order) {
int p;
if (b[i] >= a[i]) p = b[i];
else p = a[i];
int op = ceil(x, p);
if (op <= m) {
extra += (m - op);
continue;
}
int needed = min(x - m * p, extra * b[i]);
op = ceil((x - needed), p);
if (op > m) return false;
extra -= ceil(needed, b[i]);
}
return true;
}
void solve() {
int n, m;
cin >> n >> m;
vector<int> a(n), b(n);
for (int &x : a) cin >> x;
for (int &x : b) cin >> x;
vector<pi> sorting;
for (int i = 0; i < n; i++) { sorting.push_back({max(a[i], b[i]), i}); }
sort(sorting.begin(), sorting.end());
reverse(sorting.begin(), sorting.end());
vector<int> indices;
for (pi p : sorting) { indices.push_back(p.second); }
int l = 0, r = UINT64_MAX;
while (r-l>1) {
int mid = (l+r)/2;
if (is_possible(mid, a, b, indices, m)) l = mid;
else r = mid;
}
cout << l << endl;
}
signed main() {
ios::sync_with_stdio(false);
cin.tie(nullptr);
solve();
return 0;
}
