#include <bits//stdc++.h>
#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp>
using namespace std;
using namespace __gnu_pbds;
typedef tree<long long, null_type, less<long long>, rb_tree_tag,
tree_order_statistics_node_update>
ordered_set;
typedef tree<long long, null_type, less_equal<long long>, rb_tree_tag,
tree_order_statistics_node_update>
ordered_multiset;
#define ll long long
#define iloop(m, h) for (auto i = m; i != h; i += (m < h ? 1 : -1))
#define jloop(m, h) for (auto j = m; j != h; j += (m < h ? 1 : -1))
#define kloop(m, h) for (auto k = m; k != h; k += (m < h ? 1 : -1))
#define lloop(m, h) for (auto l = m; l != h; l += (m < h ? 1 : -1))
#define pll pair<ll, ll>
#define INF 1000000000000000
#define MOD1 1000000007
#define MOD2 998244353
#define MOD3 1000000009
ll n, m;
ll a[300005], b[300005];
ll lb = 0, ub = INF, mid, av, re;
int main() {
ios_base::sync_with_stdio(false);
cin.tie(NULL);
cin >> n >> m;
iloop(0, n) cin >> a[i];
iloop(0, n) {cin >> b[i]; a[i] = max(a[i], b[i]);}
while (lb < ub) {
mid = (lb + ub + 1)>>1;
av = re = 0;
iloop(0, n) {
if (a[i]*m >= mid) av += m - (mid + a[i] - 1)/a[i];
else re += (mid - a[i]*m + b[i] - 1)/b[i];
}
//cout << mid << ":" << re << " " << av << endl;
if (re > av) ub = mid - 1;
else lb = mid;
}
cout << lb;
}
