#include <iostream>
#include <stdexcept>

int capacity_for(int requested) {
    if (requested <= 0) { throw std::invalid_argument{"positive capacity required"}; }
    return requested;
}

int main() {
    try {
        int capacity = capacity_for(-2);
        std::cout << "Capacity: " << capacity << '\n';
    } catch (const std::invalid_argument& error) {
        std::cout << "Rejected: " << error.what() << '\n';
    }
}