import numpy as np

N, X = map(int, input().split())
A = tuple(map(int, input().split()))
B = tuple(map(int, input().split()))
if all(a < X for a in A):
    print(-1)
    exit()

score_sum = 0
bad_subject = []
for a, b in zip(A, B):
    if a < X:
        bad_subject.append((X - a, b))
    else:
        score_sum += a - X

L = score_sum + 1
dp = np.zeros(L, dtype=int)
for a, b in bad_subject:
    new_dp = dp + b
    new_dp[a:] = np.minimum(new_dp[a:], dp[:L - a])
    dp = new_dp
print(dp.min())