#pragma GCC optimize("O3")
#pragma GCC optimize("unroll-loops")
#include<bits/stdc++.h>
using namespace std;
typedef long long ll;
typedef long double ld;
#define REP(i, n) for (int i = 0; i < (n); ++i)
#define REPR(i, n) for (int i = n - 1; i >= 0; --i)
#define FOR(i, m, n) for (int i = m; i < n; ++i)
#define FORR(i, m, n) for (int i = m; i >= n; --i)
#define ALL(v) (v).begin(),(v).end()
#define ALLR(v) (v).rbegin(),(v).rend()
#define SORT(v) sort(ALL(v))
#define RSORT(v) sort(ALLR(v))
#define REV(v) reverse(ALL(v))
#define UNIQUE(x) SORT(x), x.erase(unique(ALL(x)), x.end())
#define fi first
#define se second
#define PB push_back
#define EB emplace_back
using pii = pair<int, int>;
using pll = pair<ll, ll>;
template <typename T> using vc = vector<T>;
template <typename T> using vvc = vector<vc<T>>;
template <typename T> using vvvc = vector<vvc<T>>;
using vi = vc<int>;
using vl = vc<ll>;
using vpi = vc<pii>;
using vpl = vc<pll>;

// noimi
#define INT(...) int __VA_ARGS__;IN(__VA_ARGS__)
#define LL(...) ll __VA_ARGS__;IN(__VA_ARGS__)
#define STR(...) string __VA_ARGS__;IN(__VA_ARGS__)
#define DBL(...) double __VA_ARGS__;IN(__VA_ARGS__)
#define VEC(type, name, size) vector<type> name(size);IN(name)
#define VEC2(type, name1, name2, size) vector<type> name1(size), name2(size);for(int i = 0; i < size; i++) IN(name1[i], name2[i])
#define VEC3(type, name1, name2, name3, size) vector<type> name1(size), name2(size), name3(size);for(int i = 0; i < size; i++) IN(name1[i], name2[i], name3[i])
#define VEC4(type, name1, name2, name3, name4, size) vector<type> name1(size), name2(size), name3(size), name4(size); for(int i = 0; i < size; i++) IN(name1[i], name2[i], name3[i], name4[i]);
#define VV(type, name, h, w) vector<vector<type>> name(h, vector<type>(w));IN(name)
int scan() { return getchar(); }
void scan(int &a) { cin >> a; }
void scan(long long &a) { cin >> a; }
void scan(char &a) { cin >> a; }
void scan(double &a) { cin >> a; }
void scan(string &a) { cin >> a; }
template <class T, class S> void scan(pair<T, S> &p) { scan(p.first), scan(p.second); }
template <class T> void scan(vector<T> &);
template <class T> void scan(vector<T> &a) {for(auto &i : a) scan(i);}
template <class T> void scan(T &a) { cin >> a; }
void IN() {}
template <class Head, class... Tail> void IN(Head &head, Tail &...tail) {scan(head);IN(tail...);}

// tute7627
template<typename T> using PQ = priority_queue<T>;
template<typename T> using QP = priority_queue<T,vector<T>,greater<T>>;
template<typename T>void stout(const T &v,ll h,ll w){for(ll i=0;i<h;i++){for(ll j=0;j<w;j++)cout<<v[i][j]<<" \n"[j==w-1];}};
template<typename T>void stout(const T &v,ll n){for(ll i=0;i<n;i++)cout<<v[i]<<" \n"[i==n-1];};
template<typename T>void stout(const vector<T>&v){stout(v,v.size());}
template<typename T>void stout(const vector<vector<T>>&v){for(auto &vv:v)stout(vv,vv.size());}
template<typename T>void debug(const T &v,ll h,ll w){for(ll i=0;i<h;i++){for(ll j=0;j<w;j++)cerr<<v[i][j]<<" \n"[j==w-1];}};
template<typename T>void debug(const T &v,ll n){for(ll i=0;i<n;i++)cerr<<v[i]<<" \n"[i==n-1];};
template<typename T>void debug(const vector<T>&v){debug(v,v.size());}
template<typename T>void debug(const vector<vector<T>>&v){for(auto &vv:v)debug(vv,vv.size());}
template<typename T>void debug(stack<T> st){while(!st.empty()){cerr<<st.top()<<" ";st.pop();}cerr<<endl;}
template<typename T>void debug(queue<T> st){while(!st.empty()){cerr<<st.front()<<" ";st.pop();}cerr<<endl;}
template<typename T>void debug(deque<T> st){while(!st.empty()){cerr<<st.front()<<" ";st.pop_front();}cerr<<endl;}
template<typename T>void debug(PQ<T> st){while(!st.empty()){cerr<<st.top()<<" ";st.pop();}cerr<<endl;}
template<typename T>void debug(QP<T> st){while(!st.empty()){cerr<<st.top()<<" ";st.pop();}cerr<<endl;}
template<typename T>void debug(const set<T>&v){for(auto z:v)cerr<<z<<" ";cerr<<endl;}
template<typename T>void debug(const multiset<T>&v){for(auto z:v)cerr<<z<<" ";cerr<<endl;}
template<typename T,size_t size>void debug(const array<T, size> &a){for(auto z:a)cerr<<z<<" ";cerr<<endl;}
template<typename T,typename V>void debug(const map<T,V>&v){for(auto z:v)cerr<<"["<<z.first<<"]="<<z.second<<",";cerr<<endl;}
int popcount(ll x){return __builtin_popcountll(x);};
int poplow(ll x){return __builtin_ctzll(x);};
int pophigh(ll x){return 63 - __builtin_clzll(x);};

void OUT() {cout << "\n";}
template <class Head, class... Tail>void OUT(Head&& head, Tail&&... tail){cout << head;if(sizeof...(tail)) cout << " ";OUT(move(tail)...);}
void ERR() {cerr << "\n";}
template <class Head, class... Tail>void ERR(Head&& head, Tail&&... tail){cerr << head;if(sizeof...(tail)) cerr << " ";ERR(move(tail)...);}
void fsp(int n){cout << fixed << setprecision(n);}
template<class T>bool chmax(T &a, const T &b) { if (a<b) { a=b; return 1; } return 0; }
template<class T>bool chmin(T &a, const T &b) { if (b<a) { a=b; return 1; } return 0; }
const ll INF=1LL<<60;
const int inf=(1<<30)-1;
const int mod=998244353;
// const int mod=1e9+7;
int dx[8]={1,0,-1,0,-1,-1,1,1};
int dy[8]={0,1,0,-1,-1,1,-1,1};

// #include<atcoder/all>
// using namespace atcoder;
// using mint=modint998244353;
// using mint=modint1000000007;

int main(){
    cin.tie(0);
    ios::sync_with_stdio(false);
    INT(n,x);
    VEC(int,a,n);
    VEC(int,b,n);
    const int vx=50000;
    vector dp(n+1,vector(vx+1,inf));
    dp[0][0]=0;
    REP(i,n){
        vector tp(n+1,vector(vx+1,inf));
        REP(j,n) REP(k,vx+1){
            if(dp[j][k]==inf) continue;
            chmin(tp[j][k],dp[j][k]+b[i]);
            chmin(tp[j+1][k+a[i]],dp[j][k]);
        }
        swap(tp,dp);
    }
    int ans=inf;
    FOR(i,1,n+1) REP(j,vx+1) if(i*x<=j) chmin(ans,dp[i][j]);
    OUT((ans==inf?-1:ans));
}