#include <iostream>
#include <cstdlib>
using namespace std;

int main()
{
	double miles {0.0};
	cout << "How many miles?\n";
	cin >> miles;

	if (!cin) {
		cerr << "sorry,that wasn't a number.\n";
		return EXIT_FAILURE;

	}

	if (miles <= 0 || miles >= 100) {
		cerr << "Sorry, that wasn't a legitimate number.\n";
		return EXIT_FAILURE;

	}

	//3 dollars, plus 70 cents for each 1/5 of a mile.
	//double dollars {3.00 + .70 * 5 * miles};
	
	double dollars {3.00 + 3.50 * miles};  //Simpler way to do the same
					       //thing

	cout << dollars << "dollars\n";
	return EXIT_SUCCESS;
}