/** - dwuy -
／＞ フ
| _ _|
／`ミ _x ノ
/ |
/ ヽ ?
／￣| | | |
| (￣ヽ＿_ヽ_)_)
＼二つ
**/
#include <bits/stdc++.h>
#define fastIO ios_base::sync_with_stdio(false); cin.tie(NULL)
#define file(a) freopen(a".inp","r",stdin); freopen(a".out", "w",stdout)
#define fi first
#define se second
#define endl "\n"
#define len(s) (int)((s).size())
#define MASK(k)(1LL<<(k))
#define TASK "test"
#define int long long
using namespace std;
typedef tuple<int, int, int> tpiii;
typedef pair<double, double> pdd;
typedef pair<int, int> pii;
typedef long long ll;
const long long OO = 1e18;
const int MOD = 1e9 + 7;
const int INF = 1e9;
const int MX = 300005;
int n, m;
int a[MX];
int b[MX];
int32_t main(){
fastIO;
//file(TASK);
cin >> n >> m;
for(int i=1; i<=n; i++) cin >> a[i];
for(int i=1; i<=n; i++) cin >> b[i];
for(int i=1; i<=n; i++) a[i] = max(a[i], b[i]);
int res = 0;
for(int lo=1, hi=OO; lo<=hi;){
int mid = (lo + hi)>>1;
int fund = 0;
for(int i=1; i<=n; i++){
int d = mid/a[i] + !!(mid%a[i]);
if(d <= m) fund += m - d;
else{
int f = mid - a[i]*m;
fund -= f/b[i] + !!(f%b[i]);
}
}
if(fund >= 0) res = mid, lo = mid + 1;
else hi = mid - 1;
}
cout << res;
return 0;
}
