#include <iostream>
#include <cstdlib>  // for EXIT_FAILURE and EXIT_SUCCESS

using namespace std;
int main() {
    int teabags;

    cout << "Enter the number of teabags: ";
    cin >> teabags;

    if (!cin) {
        cerr << "Sorry, that wasn't a valid whole number.\n";
        return EXIT_FAILURE;   // teabags die here; brewing time not born yet.
    }

    if (teabags < 1) {
        cerr << "Sorry, you must use at least 1 teabag.\n";
        return EXIT_FAILURE;   // teabags die here; brewing time not born yet.
    }

    // Brewing time formula based on number of teabags.
    int minutes {5 + 2 * (teabags - 1)};

    // Simpler expression with the same value:
    // int minutes {3 + 2 * teabags};

    cout << "Brew the tea for "
         << minutes << " minutes.\n";

    return EXIT_SUCCESS;   // teabags and minutes die here.
}