#include <iostream>
#include <iomanip>
#include <vector>
#include <cmath>
#include <algorithm>
#include <set>
#include <queue>
#include <map>
#include <unordered_map>
#include <stack>
#include <bitset>
#include <string>
#include <cstring>
#include <iterator>
#include <random>
#define ll long long
#define ld long double
#define inf (ll)(2*1e18)
#define sort(a) sort(a.begin(), a.end())
#define reverse(a) reverse(a.begin(), a.end())
#define pb push_back
#define endl "\n"
using namespace std;
bool check(ll n, ll m, ll level, vector<ll>& a, vector<ll>& b){
ll free=0;
for(int i=0;i<n;++i){
if(a[i]*m >= level){
free += m - (level + a[i] - 1)/a[i];
}else{
free -= (level - a[i]*m + b[i] - 1)/b[i];
if(free < -inf) return false;
}
}
return free >= 0;
}
void solve(){
ll n, m, i, l, r, mid;
cin>>n>>m;
vector<ll> a(n);
vector<ll> b(n);
for(i=0;i<n;++i){
cin>>a[i];
}
for(i=0;i<n;++i){
cin>>b[i];
a[i] = max(a[i], b[i]);
}
l = 0;
r = inf;
while(r - l > 1){
mid = (l+r)/2;
if(check(n, m, mid, a, b)){
l = mid;
}else{
r = mid;
}
}
cout<<l<<endl;
}
int main() {
ios_base::sync_with_stdio(false);
cin.tie(nullptr);
cout.tie(nullptr);
srand(time(nullptr));
ll t=1;
// cin>>t;
for(;t>0;--t){
solve();
}
return 0;
}
