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

public class Kappa {

    private static double logFactorial(int n){
	double fac = 0;
	for (int a = 2; a <= n; a++)
	    fac += Math.log(a);
	return fac;
    }

    private static double kappa(int n,int k,double p){
	double kappa = (k*(k-1)*Math.log(1.0/(1.0 - p)))/(2.0 *(logFactorial(n) - logFactorial(k) - logFactorial(n-k)));;
	return kappa;
    }

    private static double kappaClique(int n,int k,double p){
	double kappa = (k*(k-1)*Math.log(1.0/p))/(2.0 *(logFactorial(n) - logFactorial(k) - logFactorial(n-k)));;
	return kappa;
    }

    public static void main(String[] args) throws IOException {
	if (args.length == 0){
	    System.out.println("n p k");
	    return;
	}
	int n          = Integer.parseInt(args[0]); // vertices in a graph
	double p       = Double.parseDouble(args[1]); // edge probability
	int k          = Integer.parseInt(args[2]); // size of independent set
	System.out.println(kappaClique(n,k,p));
    }
}