#include<bits/stdc++.h>
using namespace std;
#define fi first
#define se second
#define pb push_back
#define eb emplace_back
#define vi vector<int>
#define pi pair<int,int>
#define sz(v) (int)(v).size()
#define all(v) (v).begin(), (v).end()
#define compact(v) (v).erase(unique(all(v)), (v).end())
template<class T> using upq = priority_queue<T, vector<T>, greater<T>>;
template<class T> int lwrbound(const vector<T>& a, const T& b, const int s = 0){return int(lower_bound(s + all(a), b) - a.begin());}
template<class T> int uprbound(const vector<T>& a, const T& b, const int s = 0){return int(upper_bound(s + all(a), b) - a.begin());}
#define FOR(i, a, b) for(int i = (a); i <= (b); i++)
#define ROF(i, a, b) for(int i = (a); i >= (b); i--)
#define sumof(x) accumulate(all(x), 0ll)
#define dbg(x) "[" << #x " = " << (x) << "]"
#define el "\n"
using ll = long long;
using ld = long double;
template<class T> bool ckmx(T& a, const T b){return (a < b ? a = b, true : false);}
template<class T> bool ckmn(T& a, const T b){return (a > b ? a = b, true : false);}
const ll INF = 1e18 + 1;
void Main()
{
ll n, m; cin >> n >> m;
vector<ll> A(n + 1), B(n + 1);
FOR(i, 1, n) cin >> A[i];
FOR(i, 1, n) cin >> B[i];
auto good = [&](ll Mn) -> bool{
ll days = 0;
FOR(i, 1, n){
if(A[i] < B[i]){
days += (Mn + B[i] - 1) / B[i];
}
else{
ll need = (Mn + A[i] - 1) / A[i];
ll can = min(m, need);
days += can;
ll rem = Mn - A[i] * can;
if(rem <= 0) continue;
days += (rem + B[i] - 1) / B[i];
}
if(days > m * n) return false;
}
return days <= m * n;
};
ll l = 0, r = INF;
while(l + 1 < r){
ll m = l+r>>1;
if(good(m)) l = m;
else r = m;
}
cout << l << el;
}
int32_t main()
{
ios_base::sync_with_stdio(0);
cin.tie(0); cout.tie(0);
#define name "InvMOD"
if(fopen(name".INP", "r")){
freopen(name".INP", "r", stdin);
freopen(name".OUT", "w", stdout);
}
int t = 1; while(t--) Main();
return 0;
}
