今天有做作業，根據參考程試，處理overflow之後，出現 Failed case #4/17: time limit exceeded (Time used: 1.99/1.00, memory used: 22884352/2147483648.)，今天只做到這裡，希望明天能夠解決。

#include <iostream>
#include <vector>
#include <algorithm>

long long MaxPairwiseProduct(const std::vector<int>& numbers) {
    long long max_product = 0;
    int n = numbers.size();

    for (int first = 0; first < n; ++first) {
        for (int second = first + 1; second < n; ++second) {
            max_product = std::max( max_product, 
            ( long long )   numbers[first] * numbers[second]);
        }
    }

    return max_product;
}

int main() {
    int n;
    std::cin >> n;
    std::vector<int> numbers(n);
    for (int i = 0; i < n; ++i) {
        std::cin >> numbers[i];
    }

    std::cout << MaxPairwiseProduct(numbers) << "\n";
    return 0;
}