import java.io.*;
import java.util.*;
import java.text.*;
import java.math.*;
import java.util.regex.*;

public class Solution {

    private static BigDecimal pow(BigDecimal bd, int exponent) {
        if (exponent == 1) {
            return bd;
        }
        
        //First Calculate square
        BigDecimal sq = bd.multiply(bd);
        if (exponent == 2) {
            return sq;
        }
        
        BigDecimal bd3 = new BigDecimal(1);
        while (exponent>1) {
            bd3 = bd3.multiply(sq);
            exponent -= 2;
        }
        
        if (exponent == 1) {
            bd3 = bd3.multiply(bd);
        }
        
        return bd3;
    }
  
    public static void main(String[] args) {
        Scanner in = new Scanner(System.in);
        int a = in.nextInt();
        int b = in.nextInt();
        int t = in.nextInt();
        in.close();
        
        double f = 0.5*(a+b);
        //System.out.println("f="+f);
        BigDecimal bd = new BigDecimal(f);
        //System.out.println("bd="+bd.toPlainString());
        bd = pow(bd, t);
        //System.out.println("after power bd="+bd.toPlainString());
        BigDecimal bd2 = ((new BigDecimal(10)).pow(9)).add(new BigDecimal(7));
        //System.out.println("bd2="+bd2.toPlainString());
        BigDecimal bd3 = bd.divide(bd2, BigDecimal.ROUND_DOWN).multiply(bd2);
        //System.out.println("bd3="+bd3.toPlainString());
        bd3 = bd.subtract(bd3);
        System.out.println(bd3.toPlainString());
    }
}