#include <bits/stdc++.h>
inline int two(int n) { return 1 << n; }
inline int test(int n, int b) { return (n >> b) & 1; }
inline void set_bit(int& n, int b) { n |= two(b); }
inline void unset_bit(int& n, int b) { n &= ~two(b); }
inline int last_bit(int n) { return n & (-n); }
inline int ones(int n) {
  int res = 0;
  while (n && ++res) n -= n & (-n);
  return res;
}
long long int gcd(long long int a, long long int b) {
  return (a ? gcd(b % a, a) : b);
}
long long int modPow(long long int a, long long int b, long long int MOD) {
  long long int x = 1, y = a;
  while (b > 0) {
    if (b % 2 == 1) {
      x = (x * y) % MOD;
    }
    b /= 2;
    y = (y * y) % MOD;
  }
  return x;
}
long long int modInverse(long long int a, long long int p) {
  return modPow(a, p - 2, p);
}
using namespace std;
const int N = 1001;
int n, k, ans;
int A[N], B[N];
int dp[101][200000];
int solve(int idx, int balance) {
  if (idx == n) {
    if (balance == 0) return 0;
    return -(1 << 28);
  }
  if (dp[idx][balance] != -1) return dp[idx][balance];
  int p1 = A[idx] + solve(idx + 1, balance + A[idx] - k * B[idx]);
  int p2 = solve(idx + 1, balance);
  return dp[idx][balance] = max(p1, p2);
}
int main() {
  ios::sync_with_stdio(false);
  cin.tie(0);
  cin >> n >> k;
  for (auto i = 0; i < (n); i++) cin >> A[i];
  for (auto i = 0; i < (n); i++) cin >> B[i];
  memset(dp, -1, sizeof(dp));
  ans = solve(0, 0);
  if (ans < 1)
    cout << "-1";
  else
    cout << ans;
  return 0;
}
