N,K = map(int,input().split())
A = list(map(int,input().split()))

P = [0] * 100010

for i in range(N):
	P[A[i]] += 1

A = []

for i in range(1,100010):
	for j in range(min(K // i + 1,P[i])):
		A.append(i)

N = len(A)
A.sort()
A.reverse()
B = 1
C = [0] * 100010
C[N] = (1 << K)
for i in range(N,0,-1):
	C[i - 1] = C[i] | (C[i] >> A[i - 1])
if (C[0] & 1):
	ans = 0
	for i in range(N):
		if (B & C[i + 1]) == 0:
			ans += 1;
		B |= (B << A[i])
	print(ans)
else:
	print(-1)