题目
code：
#include <bits/stdc++.h>
#define int long long
using namespace std;
const int N = 17, M = 5e6+1;
int n, k;
struct Product {
int p[N], pro[M], sz, t;
void init(char op) {
if (op == 'l') sz = n>>1;
if (op == 'r') sz = n+1>>1;
memset(pro, 0, sizeof pro);
memset(p, 0, sizeof p);
t = 0;
}
void read() {
for (int i = 1; i <= sz; ++i)
cin >> p[i];
}
void get_pro(int k, int prod) {
pro[++t] = prod;
if (k == sz+1) return ;
for (int i = 1; i < 1e18/prod; i *= p[k])
get_pro(k+1, prod*i);
}
void arrange_pro() {
sort(pro+1, pro+t+1);
t = unique(pro+1, pro+t+1)-pro-1;
}
}L, R;
bool check(int key) {
int res = 0;
for (int i = 1, j = R.t; i <= L.t; ++i) {
for (; j && R.pro[j] > key/L.pro[i]; --j);
res += j;
}
return res >= k;
}
int solve(int l, int r) {
while (l < r) {
int mid = l+r>>1;
if (check(mid)) r = mid;
if (!check(mid)) l = mid+1;
}
return r;
}
signed main() {
cin >> n;
L.init('l'), R.init('r');
L.read(), R.read();
L.get_pro(1, 1), R.get_pro(1, 1);
L.arrange_pro(), R.arrange_pro();
cin >> k; cout << solve(0, 1e18);
return 0;
}