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

public class Solution {
    static int a;
    static int b;
    
    /*private class Node(){
        int p;
        Node left;
        Node right;
        
        public Node(int p){
            this.p = p;
            this.left = null;
            this.right = null;
        }
        
        public Node(int p, Node l, Node r){
            this.p = p;
            this.left = l;
            this.right = r;
        }
    }
    
    public Node createTree(int t, int p){
        Node n = new Node(p);
        if (t == 0){
            return n;
        }
        
        t--;
        n.left = createTree(t, p*a*.5);
        n.right = createTree(t, p*b*.5);
        return n;
    }*/
    
    public static double calc(int t, double p){
        if (t == 0){
            return p;
        }
        
        t--;
        return calc(t, p*a*.5) + calc(t, p*b*.5);
    }
    
    public static void main(String[] args) {
        /* Enter your code here. Read input from STDIN. Print output to STDOUT. Your class should be named Solution. */
        Scanner scan = new Scanner(System.in);
        a = scan.nextInt();
        b = scan.nextInt();
        int t = scan.nextInt();
        
        System.out.println((int)calc(t, 1));
        //Node head = createTree(t, 1);
    }
}