// oj.uz SELF STUDY (JOI22_HO_T2)
#include <iostream>
#include <vector>
#include <utility>
#include <algorithm>
using namespace std;
using ll = long long;
const ll MAX_NUM = 1e9 * 1e9; // Ai or Bi * M
int N, M;
vector<pair<int, int>> vec;
bool ifFail(const ll passline, ll t) {
ll comprehension = 0;
int cnt_course = 0;
int cnt = M;
while(t--) {
if(comprehension < passline) {
if(vec[cnt_course].first > vec[cnt_course].second && cnt > 0) {
comprehension += vec[cnt_course].first;
cnt--;
} else comprehension += vec[cnt_course].second;
if(comprehension >= passline) {
// cout << comprehension << '\n';
cnt_course++;
comprehension = 0;
cnt = M;
}
}
}
// cout << passline << ' ' << cnt_course << '\n';
return cnt_course < N;
}
int main() {
ios::sync_with_stdio(0);
cin.tie(0); cout.tie(0);
cin >> N >> M;
int t = N * M;
vec.resize(N);
for(auto &i : vec) cin >> i.first;
for(auto &i : vec) cin >> i.second;
ll l = 1, r = MAX_NUM;
while(l < r) {
ll mid = (l + r) / 2 + 1;
if(ifFail(mid, t)) {
r = mid - 1;
}
else {
l = mid;
}
}
cout << l << '\n';
return 0;
}
