#include <bits/stdc++.h>
#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp>
using namespace __gnu_pbds;
using namespace std;
#define int long long
#define mp make_pair
#define pb push_back
#pragma GCC optimize("Ofast")
#pragma GCC optimize("unroll-loops")
#pragma GCC target("avx2")
constexpr int INF = (int)2e9;
constexpr int N = (int)4e5 + 111;
constexpr int md = (int)1e9+7;
constexpr int mdPower = (int)1e9+7 - 1;
constexpr double eps = 1e-7;
typedef __int128 _uint;
typedef long long ll;
mt19937_64 rnd(time(nullptr));
void add(int& a,int b){
a += b; if(a >= md) a -= md;
}
void sub(int& a,int b){
a -= b; while(a < 0) a += md;
}
void add(__int128& a,int b){
a += b;
}
void sub(__int128& a,int b){
a -= b;
}
int bpow(int a,int b){
if(b == 0)
return 1;
if(b % 2 == 0){
int t = bpow(a,b>>1);
return 1ll*t*t%md;
}
return 1ll * a*bpow(a,b-1) % md;
}
int inv(int a){
return bpow(a,md-2);
}
//int fac[N],invfac[N];
//
//void init(){
// fac[0] = 1;
// for(int i = 1; i < N; i++){
// fac[i] = (fac[i-1] * i) % md;
// }
// invfac[N-1] = inv(fac[N-1]);
// for(int i = N-2; i >= 0; i--){
// invfac[i] = (invfac[i+1] * (i+1))%md;
// }
// return;
//}
//
//int C(int n,int k){
// if(k > n)
// return 0;
// return fac[n] * invfac[k] % md * invfac[n-k] % md;
//}
//
//int A(int n,int k){
// if(k > n)
// return 0;
// return fac[n] * invfac[n-k] % md;
//
int n,m;
int a[N],b[N];
int cur[N];
bool f(int x){
int free = n*m;
for(int i = 0; i < n; i++){
cur[i] = 0;
}
for(int i = 0; i < n; i++){
if(a[i] > b[i]){
int t = min(m,(x + a[i] - 1)/a[i]);
free -= t;
cur[i] += t * a[i];
}
}
for(int i = 0; i < n; i++){
if(cur[i] >= x)
continue;
int t = min(free,((x-cur[i]) + b[i] - 1) / b[i]);
free -= t;
cur[i] += t * b[i];
if(cur[i] < x)
return false;
}
return true;
}
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];
}
int l = 0, r = (int)2e18;
while(r - l > 1){
int mid = (l+r)>>1;
if(f(mid))
l = mid;
else
r = mid;
}
cout << l << "\n";
return;
}
signed main(){
ios::sync_with_stdio(false);cin.tie(nullptr);cout.tie(nullptr);
int tests = 1;
// cin >> tests;
for(int test = 1; test <= tests; test++){
// cerr << "test = " << test << "\n";
solve();
}
return 0;
}
/**
**/
