#include <cstdio>
#include <stdio.h>
#include <stdbool.h>
#include <iostream>
#include <map>
#include <vector>
#include <climits>
#include <stack>
#include <string>
#include <queue>
#include <algorithm>
#include <set>
#include <unordered_set>
#include <unordered_map>
#include <cmath>
#include <cctype>
#include <bitset>
#include <iomanip>
#include <cstring>
#include <numeric>
#include <cassert>
using namespace std;
#define int long long
#define pii pair<int, int>
#define mp make_pair
#define pb push_back
#define fi first
#define se second
int32_t main(){
ios_base::sync_with_stdio(0);
cin.tie(0);
cout.tie(0);
int n, m;
cin>>n>>m;
vector<pii> vect(n);
for (int i=0; i<n; ++i)cin>>vect[i].fi;
for (int i=0; i<n; ++i)cin>>vect[i].se, vect[i].fi=max(vect[i].fi, vect[i].se);
int low=-1, high=LLONG_MAX/2;
while (low+1<high){
int mid=(low+high)/2;
__int128 c=0;
for (int i=0; i<n; ++i)c+=min((mid+vect[i].fi-1)/vect[i].fi, m)+max(0ll, ((mid-vect[i].fi*m)+vect[i].se-1)/vect[i].se);
if (c<=n*m)low=mid;
else high=mid;
}
cout<<low;
}
