from fractions import Fraction
import math
n,a,b=map(int,input().split())
ans=Fraction(0,1)
for i in range(n+1):
  k=int(input())
  ans+=Fraction(k*b**(i+1),(i+1))
  ans-=Fraction(k*a**(i+1),(i+1))
print(ans.numerator//ans.denominator)