from fractions import*
n,a,b,*k=[*map(int,open(0).read().split())]
def f(x):
  ret=0
  i=1
  for nk in k:
    ret+=Fraction(nk*(x**i),i)
    # print(nk,x,i,i+1)
    i+=1
  return ret
ans=f(b)-f(a)
x,y=ans.numerator,ans.denominator
print(x//y)