from fractions import Fraction
N,S,id = map(int,input().split())
A = list(map(int,input().split()))
writer = A.pop(id) + 100 * S
A.sort()
A.reverse()
P = 1
for ai,a in enumerate(A):
	p = 0
	for i in range(1,N + 1):
		j = 50 * S * Fraction(18 + 2 * i, 8 + 2 * i)
		if j + a > writer:
			p = p + 1
		else:
			break
		print(p)
	P = P * (1 - Fraction(p,N - ai - 1))
	if P == 0:
		break
print(float(P))