n, x = map(int, input().split())
A = list(map(int, input().split()))
B = list(map(int, input().split()))

INF = 10**18
s = sum(A)
from collections import defaultdict
dp = defaultdict(lambda: INF)
dp[(0, 0)] = 0
for a, b in zip(A, B):
    nx = defaultdict(lambda: INF)
    for (i, j), v in dp.items():
        nx[(i+1, j+a)]  =min(nx[(i+1, j+a)], v)
        nx[(i, j)] = v+b
    dp = nx

ans = INF
for (i, j), v in dp.items():
    if i == 0:
        continue
    if j >= x*i:
        ans = min(ans, v)
if ans != INF:
    print(ans)
else:
    print(-1)