#include <bits/stdc++.h>
using namespace std;
using ll = long long;
using ld = long double;
#define fi first
#define se second
#define vi vector<int>
#define vll vector<long long>
#define pii pair<int, int>
#define pll pair<long long, long long>
#define pb push_back
#define mp make_pair
#define eb emplace_back
#define all(x) (x).begin(), (x).end()
#define sz(x) (int)(x).size()
mt19937 rng(chrono::high_resolution_clock::now().time_since_epoch().count());
mt19937_64 rng64(chrono::high_resolution_clock::now().time_since_epoch().count());
inline int rand(int l,int r){return uniform_int_distribution<int>(l, r)(rng);}
inline ll rand(ll l,ll r){return uniform_int_distribution<ll>(l, r)(rng64);}
#ifdef DEBUG
auto&operator<<(auto&o,pair<auto,auto>p){return o<<"("<<p.first<<", "<<p.second<<")";}
auto operator<<(auto&o,auto x)->decltype(x.end(),o){o<<"{";int i=0;for(auto e:x)o<<","+!i++<<e;return o<<"}";}
#define debug(X...)cerr<<"["#X"]: ",[](auto...$){((cerr<<$<<"; "),...)<<endl;}(X)
#else
#define debug(...){}
#endif
struct custom_hash {
static uint64_t splitmix64(uint64_t x) {
x += 0x9e3779b97f4a7c15;
x = (x ^ (x >> 30)) * 0xbf58476d1ce4e5b9;
x = (x ^ (x >> 27)) * 0x94d049bb133111eb;
return x ^ (x >> 31);
}
size_t operator()(uint64_t x) const {
static const uint64_t FIXED_RANDOM = chrono::steady_clock::now().time_since_epoch().count();
return splitmix64(x + FIXED_RANDOM);
}
};
const int MAXN = 3e5 + 7;
ll a[MAXN];
ll b[MAXN];
int n;
ll m;
bool check(ll k){
ll days = (ll)n * m;
for(int i = 1; i <= n; i++){
if(a[i] <= b[i]){
ll cnt = (ll)(k + b[i] - 1) / b[i];
days = (ll)days - cnt;
}else{
ll cnt1 = (ll)(k + a[i] - 1) / a[i];
//cout << cnt1 << ' ';
if(cnt1 <= m){
days = (ll)days - cnt1;
}else{
days = (ll)days - m - (ll)((ll)k - (ll)m * a[i] + b[i] - 1) / b[i];
}
}
//cout << days << '\n';
if(days < 0LL){
return 0;
}
}
return 1;
}
int main(){
ios_base::sync_with_stdio(0);
cin.tie(NULL);
cout.tie(NULL);
cin >> n >> m;
for(int i = 1; i <= n; i++){
cin >> a[i];
}
for(int i = 1; i <= n; i++){
cin >> b[i];
}
ll l = 0LL;
ll p = (ll)1e18;
ll s;
while(l < p){
s = (ll)(l + p + 1) / 2;
if(check(s)){
l = s;
}else{
p = s - 1;
}
}
cout << l << '\n';
//cout << check(21);
return 0;
}
