/*#pragma GCC optimize("O3")
#pragma GCC optimization("Ofast,unroll-loops")
#pragma GCC target("avx2,bmi,bmi2,lzcnt,popcnt")*/
#include <bits/stdc++.h>
/*#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp>*/
#define ll long long
#define ll1 long long
#define ull unsigned long long
#define dou long double
#define str string
#define vll vector<ll>
#define vi vector<int>
#define pll pair<ll, ll>
#define vpll vector<pll>
#define vbool vector<bool>
#define vstr vector<str>
#define vvll vector<vll>
#define pb push_back
#define pf push_front
#define endl "\n"
#define fr first
#define se second
// #define sortcmp(a) sort(a.begin(), a.end(), cmp)
#define sort(a) sort(a.begin(), a.end())
#define reverse(a) reverse(a.begin(), a.end())
#define speed ios_base::sync_with_stdio(0);cin.tie(0);cout.tie(0)
#define INF 1000000000000000007
#define ordered_set tree<ll, null_type, less_equal<ll>, rb_tree_tag, tree_order_statistics_node_update>
using namespace std;
//using namespace __gnu_pbds;
mt19937 rng(time(0));
ll randll(ll l, ll r) {
return uniform_int_distribution<ll>(l, r)(rng);
}
int main(){
speed;
srand(time(0));
ll n, m;
cin >> n >> m;
vll a(n), b(n);
for (int i =0 ; i < n; i ++) {
cin >> a[i];
}
for (int i =0 ; i < n; i ++) {
cin >> b[i];
a[i] = max(a[i], b[i]);
}
ll l = 0, r = INF;
while (r-l > 1) {
ll x = (l+r)/2;
ll k = n*m;
bool q = 1;
for (int i = 0; i < n; i ++) {
ll k1 = x/a[i]+(x % a[i] != 0);
if (k1 > k) {
q = 0;
break;
}
if (k1 > m) {
k -= m;
ll x1 = x-m*a[i];
ll k1 = x1/b[i]+(x1 % b[i] != 0);
if (k1 > k) {
q = 0;
break;
}
k -= k1;
}
else {
k -= k1;
}
}
if (q) l = x;
else r = x;
}
cout << l << endl;
}
