#include <bits/stdc++.h>
using namespace std;
#define int long long
#define FOR(i, l, r) for(int i = (l); i < (r); ++i)
#define ROF(i, r, l) for(int i = (r) - 1; i >= (l); --i)
#define mp make_pair
#define mt make_tuple
#define ff first
#define ss second
#define all(v) begin(v), end(v)
#define rall(v) rbegin(v), rend(v)
#define pb push_back
#define eb emplace_back
#define sz(v) (int)v.size()
#define sum_of(v) accumulate(all(v), 0ll)
#define compact(v) v.erase(unique(all(v)), end(v))
#define dbg(x) "[" #x " = " << (x) << "]"
template<typename T>
bool minimize(T& a, const T& b){
if(a > b) return a = b, true;
return false;
}
template<typename T>
bool maximize(T& a, const T& b){
if(a < b) return a = b, true;
return false;
}
using ll = long long;
using db = double;
using ld = long double;
using ull = unsigned long long;
using pi = pair<int, int>;
using pl = pair<ll, ll>;
using pd = pair<db, db>;
using vi = vector<int>;
using vb = vector<bool>;
using vc = vector<char>;
using vl = vector<ll>;
using vd = vector<db>;
using vpi = vector<pi>;
using vpl = vector<pl>;
void setIO(){
ios_base::sync_with_stdio(0); cin.tie(0);
#ifdef LOCAL
freopen("task.inp", "r", stdin);
freopen("task.out", "w", stdout);
#endif // LOCAL
}
const int MAX = 2e5 + 5;
signed main(){
setIO();
int N, M;
cin >> N >> M;
vi A(N), B(N);
FOR(i, 0, N) cin >> A[i];
FOR(i, 0, N) cin >> B[i];
ll l = 1, r = 1e18, ans = -1;
while(l <= r){
ll mid = l + r >> 1;
ll uses = 0;
FOR(i, 0, N){ //fucking overflowing
if(A[i] <= B[i]){
uses += (mid + B[i] - 1) / B[i];
if(uses > 1LL * N * M) break;
continue;
}
if(1LL * M * A[i] >= mid){
uses += (mid + A[i] - 1) / A[i];
if(uses > 1LL * N * M) break;
continue;
}
uses += M;
uses += (mid - 1LL * A[i] * M + B[i] - 1) / B[i];
if(uses > 1LL * N * M) break;
}
if(uses <= 1LL * N * M) ans = mid, l = mid + 1;
else r = mid - 1;
}
assert(ans != -1);
cout << ans << '\n';
return 0;
}
