#include "bits/stdc++.h"
using namespace std;
void abc() {cout << endl;}
template <typename T, typename ...U> void abc(T a, U ...b) {
cout << a << ' ', abc(b...);
}
template <typename T> void printv(T l, T r) {
while (l != r) cout << *l << " \n"[++l == r];
}
template <typename A, typename B> istream& operator >> (istream& o, pair<A, B> &a) {
return o >> a.first >> a.second;
}
template <typename A, typename B> ostream& operator << (ostream& o, pair<A, B> a) {
return o << '(' << a.first << ", " << a.second << ')';
}
template <typename T> ostream& operator << (ostream& o, vector<T> a) {
bool is = false;
for (T i : a) {o << (is ? ' ' : '{'), is = true, o << i;}
return o << '}';
}
#ifdef local
#define test(args...) abc("[" + string(#args) + "]", args)
#else
#define test(args...) void(0)
#endif
using ll = long long;
ll n, m;
ll a[300005], b[300005];
bool able(ll target) {
ll debt = 0;
for (int i = 0; i < n; i++) {
if (a[i] * m >= target) {
debt -= m - (target + a[i] - 1) / a[i];
} else {
debt += (target - a[i] * m + b[i] - 1) / b[i];
}
if (debt > n*m) return false;
}
return (debt <= 0);
}
int main() {
ios_base::sync_with_stdio(0);
cin.tie(0); cout.tie(0);
// freopen("", "r", stdin);
// freopen("", "w", stdout);
cin >> n >> m;
for (int i = 0; i < n; i++) cin >> a[i];
for (int i = 0; i < n; i++) cin >> b[i];
for (int i = 0; i < n; i++) a[i] = max(a[i], b[i]);
ll l = 0, r = 1e18;
ll ans = 0;
// cout << able(12) << endl;
while (l <= r) {
ll mid = (l + r) / 2;
// cout << l << " " << r << " " << mid << endl;
if (able(mid)) {
ans = mid;
l = mid + 1;
} else r = mid - 1;
}
cout << ans;
}
