#include "bits/stdc++.h"
using namespace std;
#define ll long long
#define ln '\n'
const int N = 3e5 + 5;
const ll INF = 5e18 + 5;
ll n, m, a[N], b[N];
inline ll ceil(ll x, ll y) {return (x + y - 1) / y;}
ll cnt(ll go_lesson, ll i, ll tar){
return (m - go_lesson) - max(0LL, ceil(tar - a[i] * go_lesson, b[i]));
}
void solve(){
cin >> n >> m;
for (int i = 0; i < n; i++) cin >> a[i];
for (int i = 0; i < n; i++) cin >> b[i];
// ll l = 7, r = 7, ans = 0;
ll l = 0, r = INF, ans = 0;
while (l <= r){
ll tar = (l + r) / 2;
ll free, need; free = need = 0;
for (int i = 0; i < n; i++){
if (b[i] >= a[i]) {
free += m;
need += ceil(tar, b[i]);
} else {
// maybe don't blindly go to lessons
ll lf = 0, rt = m, glit = 0;
while (glit++ < 40){
ll tl = (2 * lf + rt) / 3;
ll tr = (lf + 2 * rt) / 3;
if (cnt(tl, i, tar) > cnt(tr, i, tar)) rt = tr;
else lf = tl;
}
ll best = lf;
for (ll j = max(0LL, lf - 100); j <= min(m, lf + 100); j++){
if (cnt(j, i, tar) > cnt(best, i, tar)) best = j;
}
free += m - best;
need += max(0LL, ceil(tar - a[i] * best, b[i]));
}
// cout << need << ' ' << free << ln;
}
if (need <= free) {ans = tar; l = tar + 1;}
else r = tar - 1;
}
cout << ans << ln;
}
int main() {
ios_base::sync_with_stdio(false);
cin.tie(NULL);
// int TT; cin >> TT;
// while (TT--) {solve();}
solve();
}
