/* package whatever; // don't place package name! */

import java.util.*;
import java.lang.*;
import java.io.*;

class Ideone
{
	public static void main (String[] args) throws java.lang.Exception
	{
		Scanner x = new Scanner(System.in); 
		double R,R1,R2,R3;
		R1 = x.nextDouble();
		R2 = x.nextDouble();
		R3 = x.nextDouble();
		R = (1/R1)+(1/R2)+(1/R3);
		System.out.format("Общее сопротивление цепи = %f (Ом)",R);
		
		
	}
}