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

int main(){
	double miles {0.0};
	cout<< "Enter the miles traveled(it has to be greater than 0):\n";
	cin >> miles;

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

	if (miles < 0 ){
		cerr << "Sorry, the fee can't below or equal to zero.\n";
		return EXIT_FAILURE;
	}

	double fee = (miles*3.5 + 3);

	cout << miles << "miles of trip will cost you: "
		<< fee << " dollars.\n";

	return EXIT_SUCCESS;
}