#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
typedef long double ld;
typedef unsigned long long ull;
#define len(v) (int)((v).size())
const int inf = 1e9;
inline void solve(){
ll n, m;
cin >> n >> m;
vector<ll> a(n);
for (int i = 0; i < n; ++i){
cin >> a[i];
}
vector<ll> b(n);
for (int i = 0; i < n; ++i){
cin >> b[i];
}
for (int i = 0; i < n; ++i){
a[i] = max(a[i], b[i]);
}
ll li = 0, ri = 2e18 + 7;
while (ri - li > 1){
ll mi = (li + ri) / 2;
ll bl = n * m;
for (int i = 0; i < n && bl >= 0; ++i){
ll us = min(m, (mi + a[i] - 1) / a[i]);
ll rm = max(0ll, mi - us * a[i]);
bl -= us;
bl -= (rm + b[i] - 1) / b[i];
}
if (bl >= 0){
li = mi;
}
else{
ri = mi;
}
}
cout << li << '\n';
}
signed main() {
ios_base::sync_with_stdio(false);
cin.tie(nullptr);
cout.tie(nullptr);
cout.precision(60);
int t = 1;
// cin >> t;
while (t--) {
solve();
}
}
