import java.util.Scanner;
import java.text.DecimalFormat;

public class Resistencia {
    public static void main(String[] args) {
        int i = 0;
        double[] resistances = new double[3];

        while(i < 3) {
            Scanner sc = new Scanner(System.in);
            System.out.println(String.format("Ingrese resistencia %d:", i+1));

            String resistance = sc.nextLine();
            double resistance_as_long = Double.parseDouble(resistance);

            if (resistance_as_long > 0){
                double processed_resistance = 1/resistance_as_long;
                resistances[i] = processed_resistance;
                i++;
            }
            else {
                System.out.println("------------------------");
                System.out.println("Ingrese un número positivo");
                System.out.println("------------------------");
                continue;
            }
        }

        double resistances_sum = resistances[0] + resistances[1] + resistances[2];
        double total_resistance = 1/resistances_sum;

        System.out.println("------------------------");
        DecimalFormat df = new DecimalFormat("#.##");
        System.out.println("La resistencia total es de " + df.format(total_resistance));
    }
}