package main

import . "fmt"
import . "math/big"

func main() {
	var n int64
	a,b := new(Rat),new(Rat)
	Scan(&n,a,b)
	sum := NewRat(0,1)
	ax,bx := NewRat(1,1), NewRat(1,1)
	for i:=int64(1); i<=n+1; i++ {
		var k int64
		Scan(&k)
		ax.Mul(ax, a)
		bx.Mul(bx, b)
		sum.Add(sum, new(Rat).Mul(NewRat(k, i), new(Rat).Sub(bx,ax)))
	}
	// Println(sum)
	Println(new(Int).Div(sum.Num(), sum.Denom()))
	// Println(new(Float).SetRat(sum))
}