#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) {
	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 + 3.50 * miles};

cout << dollars << " dollars\n";

return EXIT_SUCCESS;

}