//#pragma optimize("Ofast")
//#pragma optimize("unroll-loops")
//#pragma traget("avx,avx2")
#include <iostream>
#include <cmath>
#include <algorithm>
#include <stdio.h>
#include <cstdint>
#include <cstring>
#include <string>
#include <cstdlib>
#include <vector>
#include <bitset>
#include <map>
#include <queue>
#include <ctime>
#include <stack>
#include <set>
#include <list>
#include <random>
#include <deque>
#include <functional>
#include <iomanip>
#include <sstream>
#include <fstream>
#include <complex>
#include <numeric>
#include <cassert>
#include <array>
#include <tuple>
#include <unordered_map>
#include <unordered_set>
#include <thread>
typedef long long ll;
typedef unsigned long long ull;
typedef long double ld;
#define el '\n'
#define ff first
#define ss second
#define pb push_back
#define pf push_front
#define popb pop_back
#define popf pop_front
#define point pair <ll, ll>
#define all(x) x.begin(), x.end()
#define rall(x) x.rbegin(), x.rend()
using namespace std;
#include <random>
mt19937 rnd(time(0));
const ll INF = 1e18 + 10;
const ll inf = 1e9 + 10;
const ll N = 1e6 + 10;
const ll mod = 1e9 + 7;
const ll LOG = 20;
const ll K = 1e3 + 20;
void solve() {
ll n, m;
cin >> n >> m;
vector <ll> a(n), b(n);
for (ll i = 0; i < n; i++)
cin >> a[i];
for (ll i = 0; i < n; i++)
cin >> b[i];
ll l = 0, r = INF;
while (l + 1 < r) {
ll mid = (l + r) >> 1;
ll cnt = 0;
bool ok = 1;
for (ll i = 0; i < n; i++) {
if (a[i] > b[i]) {
if (a[i] * m >= mid)
cnt += (mid + a[i] - 1) / a[i];
else
cnt += m + (mid + b[i] - 1 - a[i] * m) / b[i];
} else {
cnt += (mid + b[i] - 1) / b[i];
}
if (cnt > n * m) {
ok = 0;
break;
}
}
if (ok)
l = mid;
else
r = mid;
}
cout << l << el;
return;
}
signed main() {
ios_base::sync_with_stdio(0);
cin.tie(0); cout.tie(0);
int tests = 1;
//cin >> tests;
while (tests--)
solve();
return 0;
}
/*
*/
