#include <iostream>
#include <set>
#include <algorithm>
using namespace std;
const int nmax = 3e5 + 7;
int v[nmax], b[nmax], cnt[nmax], n, k;
long long unu = 1;
struct pairing {
long long first;
int second;
const bool operator < (pairing a) const {
if(first != a.first) {
return first < a.first;
} else {
return second > a.second;
}
}
};
bool check(long long x) {
long long sum = 0;
for(int i = 1; i <= n; i ++) {
long long curr = x / v[i];
if(v[i] * curr < x) {
curr ++;
}
sum += curr;
}
if(sum <= n * k) {
return 1;
}
return 0;
}
int32_t main() {
int test = 1;
cin >> n >> k;
for(int i = 1; i <= n; i ++) {
cin >> v[i];
}
for(int i = 1; i <= n; i ++){
cin >> b[i];
if(v[i] != b[i]) {
test = 1;
}
}
if(!test) {
long long l = 0, r = 1e18;
int opr = 0;
while(l < r) {
opr ++;
long long mid = (l + r) / 2;
if(check(mid) == 1) {
l = mid + 1;
} else {
r = mid - 1;
}
if(opr == 100) {
break;
}
}
cout << max(unu, r);
return 0;
}
set<pairing> pq;
for(int i = 1; i <= n; i ++) {
pq.insert({max(v[i], b[i]), i});
cnt[i] = 1;
}
for(int i = 2; i <= k; i ++) {
for(int j = 1; j <= n; j ++) {
pairing curr = *(pq.begin());
long long sum = curr.first;
int ind = curr.second;
pq.erase({sum, ind});
if(cnt[ind] < k) {
sum += max(v[ind], b[ind]);
cnt[ind] ++;
} else {
sum += b[ind];
}
pq.insert({sum, ind});
}
}
long long minn = 1e18;
for(auto it : pq) {
// cout << it.first << " " << it.second << endl;
minn = min(minn, it.first);
}
cout << minn;
return 0;
}
