#pragma GCC optimize("Ofast")
#include <bits/stdc++.h>
using namespace std;
#define int __int128
#define pii pair<int,int>
#define p_q priority_queue
#define endl '\n'
#define pb push_back
unsigned long long n, m;
vector<unsigned long long> a, b;
bool check(int mid) {
int rem = n*m;
for (int i = 0; i < n; ++i) {
if (a[i] > b[i]) {
if (a[i]*m >= mid) {
rem -= mid/a[i]+(mid%a[i] != 0);
} else {
int cur = mid-a[i]*m;
rem -= m;
rem -= cur/b[i]+(cur%b[i] != 0);
}
} else {
rem -= mid/b[i]+(mid%b[i] != 0);
}
}
return rem >= 0;
}
signed main() {
ios::sync_with_stdio(0), cin.tie(0), cout.tie(0);
cin>>n>>m;
a.resize(n), b.resize(n);
for (auto& i : a) cin>>i;
for (auto& i : b) cin>>i;
int l = 0, r = 4e36;
while(r-l > 1) {
int mid = r+(l-r)/2;
if (check(mid)) l = mid;
else r = mid;
}
unsigned long long ans = l;
cout<<ans<<endl;
return 0;
}
