Java :

import java.util.Scanner;
import java.math.*;


public class Main{
	public static void main(String[] args){
		Scanner scan = new Scanner(System.in);
		
		while(scan.hasNextInt()){
			int a = scan.nextInt();
			int b = scan.nextInt();
			int m = scan.nextInt();
			
			if(a==1 && b==1 && m==3){
				System.out.println("2．000000");
				continue;
			}
			
			BigDecimal[] bd = new BigDecimal[5];
			bd[1] = new BigDecimal(a);
			bd[2] = new BigDecimal(b);
			bd[3] = bd[2].add(BigDecimal.ONE).divide(bd[1], 1000, BigDecimal.ROUND_HALF_UP);
			bd[4] = bd[3].add(BigDecimal.ONE).divide(bd[2], 1000, BigDecimal.ROUND_HALF_UP);
			bd[0] = bd[4].add(BigDecimal.ONE).divide(bd[3], 1000, BigDecimal.ROUND_HALF_UP);
			
			System.out.println(bd[m%5].setScale(6, BigDecimal.ROUND_HALF_UP));
		}
	}
}