#include<bits/stdc++.h>
using namespace std;
using ll = long long;
const int N = 3e5 + 10;
ll n, m;
ll A[N], B[N];
ll divi(ll a, ll b) {
return (a + b - 1) / b;
}
bool check(ll x) {
ll s = 0;
for(int i = 0; i < n; i++) {
if(B[i] >= A[i]) {
s += divi(x, B[i]);
} else {
ll t = min(m, divi(x, A[i]));
s += t + divi(max(x - t * A[i], 0ll), B[i]);
}
}
return (s <= n * m);
}
const ll INF = 1000000000000000000;
ll solve() {
ll l = 0, r = INF;
while(r - l > 1) {
ll mid = (l + r) / 2;
if(check(mid)) l = mid;
else r = mid;
}
return l;
}
// mt19937 rnd(14941);
// uniform_int_distribution<ll> ui(1, INF);
// void gen() {
// for(int i = 0; i < n; i++)
// A[i] = rnd();
// for(int i = 0; i < n; i++)
// B[i] = rnd();
// }
ll stupid() {
ll mx = (ll)1e18;
for(int i = 0; i < n; i++)
mx = min(mx, max(A[i], B[i]));
return mx;
}
int main() {
ios::sync_with_stdio(0);
cin.tie(0);cout.tie(0);
cin >> n >> m;
for(int i = 0; i < n; i++)
cin >> A[i];
for(int i = 0; i < n; i++)
cin >> B[i];
cout << stupid();
// cout << solve();
// int t = 1000;
// do {
// gen();
// t--;
// }
// while(stupid() == solve() && t);
// for(int i = 0; i < n; i++)
// cout << A[i] << ' ';
// cout << '\n';
// for(int i = 0; i < n; i++)
// cout << B[i] << ' ';
// cout << '\n';
// cout << "slow: " << stupid() << '\n';
// cout << "fast: " << solve() << '\n';
}
