#include <bits/stdc++.h>
#pragma GCC optimize(2)
#define ll long long
#define MAX_N 3000005
#define MAX_M 45
using namespace std;

ll n, k, factors[MAX_M], partialProducts[MAX_N], totalCount = 0, results[MAX_N], resultCount = 0;
ll MAX_LIMIT = 1e18;

void generateSubsets(int index, bool isOdd, ll currentProduct) {
    if (isOdd) {
        results[++resultCount] = currentProduct;
    } else {
        partialProducts[++totalCount] = currentProduct;
    }

    if (index > n) {
        return;
    }

    for (ll i = 1;; i *= factors[index]) {
        if (MAX_LIMIT / i < currentProduct) break;
        generateSubsets(index + 2, isOdd, currentProduct * i);
    }
}

bool canAchieveKthSmallestProduct(ll mid) {
    ll left = 1, right = resultCount, sum = 0;
    while (left <= totalCount) {
        while (results[right] > mid / partialProducts[left] && right >= 1) right--;
        sum += right;
        left++;
    }
    return sum >= k;
}

int main() {
    cin >> n;
    for (int i = 1; i <= n; i++) {
        cin >> factors[i];
    }
    sort(factors + 1, factors + n + 1);
    cin >> k;

    generateSubsets(1, false, 1);
    generateSubsets(2, true, 1);

    sort(partialProducts + 1, partialProducts + totalCount + 1);
    sort(results + 1, results + resultCount + 1);

    totalCount = unique(partialProducts + 1, partialProducts + totalCount + 1) - partialProducts - 1;
    resultCount = unique(results + 1, results + resultCount + 1) - results - 1;

    ll left = 0, right = 1e18;
    while (left < right) {
        ll mid = (left + right) / 2;
        if (canAchieveKthSmallestProduct(mid)) {
            right = mid;
        } else {
            left = mid + 1;
        }
    }

    cout << right;
    return 0;
}