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

class Main
{
	static Scanner sc = new Scanner(System.in);
	
	public static void main (String[] args) throws java.lang.Exception
	{
		int n, m;
		n = sc.nextInt();
		m = sc.nextInt();
		double r = sc.nextDouble();
		double[][] a = new double[n][m];
		for(int i = 0; i < n; i++){
			for(int j = 0; j < m; j++){
				a[i][j] = sc.nextDouble();
			}
		}
		double sum = 0;
		for(int i = 0; i < n; i++){
			double b = 0.5;
			for(int j = 0; j < m; j++){
				if(a[i][j] > 0){
					b = a[i][j];
					break;
				}
			}
			sum += b*Math.pow(r, n-i-1);
		}
		System.out.println(sum);
	}
}