/* Written 7/12/07 by Ross Byers
 * Contains a solution to the contest problem dive.doc
 */
 
 import java.lang.*;
 import java.util.*;
 import java.io.*;
 
 public class dive
 {
 	public static void main(String[] args) throws IOException
 	{
 		Scanner inFile = new Scanner(new File("dive.in"));
 		double rate;
 		double tank;
 		int pressure;
 		
 		// Get the input.
 		rate = inFile.nextDouble();
 		tank = inFile.nextDouble();
 		pressure = inFile.nextInt();
 		
 		// Find the compression ratio.
 		double ratio = pressure/14.0;
 		
 		// Calculate the volume of regular air in the tank, then
 		// divide this by how much air Bob uses in a minute. To
 		// get the final output in hours, divide by 60 (minutes in
 		// a hour)
 		double time = ratio * tank / rate/ 60;
 		System.out.println(time);
 	}
 }