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

public class Solution {

    public static void main(String[] args) {
        Scanner input = new Scanner(System.in);
        int a = input.nextInt();
        int b = input.nextInt();
        int t = input.nextInt();
        
        float mult = (a+b)/2;
        double ans = Math.pow(mult, t);
        
        System.out.println(ans);
    }
}