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

INF = 10**18
s = sum(A)

dp = [[INF]*(s+1) for i in range(n+1)]
dp[0][0] = 0
for a, b in zip(A, B):
    for j in reversed(range(n)):
        for k in reversed(range(s+1)):
            if dp[j][k] == INF:
                continue
            dp[j+1][k+a] = min(dp[j+1][k+a], dp[j][k])
            dp[j][k] += b
ans = INF
for j in range(1, n+1):
    for k in range(s+1):
        if k >= x*j:
            ans = min(ans, dp[j][k])
if ans != INF:
    print(ans)
else:
    print(-1)