#include <iostream>
#include <iomanip>
#include <vector>
#include <cmath>
#include <algorithm>
#include <set>
#include <queue>
#include <map>
#include <stack>
#include <bitset>
#include <string>
#include <cstring>
#include <iterator>
#include <random>
using namespace std;
typedef long long ll;
typedef pair<ll, ll> pll;
typedef long double ld;
const ll dim = 1e6+7;
const ll inf = 1e18 + 77;
#define endl "\n"
#define fi first
#define pb push_back
#define se second
#define vll vector<ll>
ll n, m;
ll a[dim], b[dim];
ll check(ll val){
__int128 free=0;
vector<pll> v;
for(int i=1; i<=n; i++){
ll f=m-(val+a[i]-1)/a[i];
if(f>0)free+=f;
else{
free-=(val-a[i]*m-1+b[i])/b[i];
}
}
if(free<0)return 0;
return 1;
}
int main() {
ios_base::sync_with_stdio(0); cin.tie(0); cout.tie(0);
cin>>n>>m;
for(int i=1; i<=n; i++) {
cin>>a[i];
}
for(int i=1; i<=n; i++) {
cin>>b[i];
a[i]=max(a[i], b[i]);
}
ll l=1;
ll r=1e18;
while(r-l>=1){
ll mid=(l+r+1)/2;
if(check(mid)){
l=mid;
}
else{
r=mid-1;
}
}
cout<<l<<endl;
return 0;
}
