# include <stdio.h>

 # include <string.h>

 # include <iostream>

 # include <algorithm>

 // # include <bits/stdc++.h>

 using namespace std;

 typedef long long ll;

 typedef long double ld;

 typedef unsigned long long ull;

 const int N = 3e4 + , M = 6e4 + ;

 const int mod = 1e9+;

 int n, m, A[N * ], B[N * ], head[N], nxt[M], to[M], tot = ;

 inline void add(int u, int v) {

     ++tot; nxt[tot] = head[u]; head[u] = tot; to[tot] = v;

 }

 inline void adde(int u, int v) {

     add(u, v), add(v, u);

 }

 int dep[N], mxd[N], son[N], sz[N];

 inline void pre_dfs(int x, int fa = ) {

     dep[x] = dep[fa] + ;

     mxd[x] = dep[x]; son[x] = ;

     for (int i=head[x]; i; i=nxt[i]) {

         if(to[i] == fa) continue;

         pre_dfs(to[i], x);

         if(mxd[to[i]] > mxd[x]) mxd[x] = mxd[to[i]], son[x] = to[i];

     }

     sz[x] = mxd[x] - dep[x];

 }

 int pos[N], idx;

 inline void pre_pos(int x, int fa = ) {

     pos[x] = ++idx;

     if(son[x]) pre_pos(son[x], x);

     for (int i=head[x]; i; i=nxt[i])

         if(to[i] != fa && to[i] != son[x]) pre_pos(to[i], x);

 }

 double mid_check, ans;

 double dp[N], tag[N];

 inline void solve(int x, int fa = ) {

     double *f = &dp[pos[x]], C = (double)A[x] - mid_check * B[x];

     if(son[x] == ) {    //leaf

         f[] = ; tag[x] = C;

         if(m == ) ans = min(ans, tag[x]);

         return ;

     }

     solve(son[x], x); f[] = -tag[son[x]];

     tag[x] = tag[son[x]] + C;

     for (int i=head[x], y; i; i=nxt[i]) {

         if(to[i] == fa || to[i] == son[x]) continue;

         solve(y = to[i], x);

         double *g = &dp[pos[y]];

         for (int j=; j<=sz[y] && j<m; ++j)

             if(m--j <= sz[x]) ans = min(ans, f[m--j] + tag[x] + g[j] + tag[y]);

          for (int j=; j<=sz[y]; ++j) f[j+] = min(f[j+], g[j] + tag[y] + C - tag[x]);

     }

     if(m <= sz[x]) ans = min(ans, f[m] + tag[x]);

 }

 inline bool chk(double x) {

      ans = 1e18; mid_check = x;

      solve();

     return ans <= ;

 }

 int main() {

     freopen("cdcq_b.in", "r", stdin);

     freopen("cdcq_b.out", "w", stdout);

     cin >> n >> m;

     for (int i=; i<=n; ++i) scanf("%d", A+i);

     for (int i=; i<=n; ++i) scanf("%d", B+i);

     if(m == -) {

         double ans = 1e18;

         for (int i=; i<=n; ++i) ans = min(ans, (double)A[i]/B[i]);

         printf("%.2lf\n", ans);

         return ;

     }

     for (int i=, u, v; i<n; ++i) {

         scanf("%d%d", &u, &v);

         adde(u, v);

     }

     --m;

     pre_dfs();

     pre_pos();

     double l = , r = 1e11, mid;

     while(r-l > 1e-) {

         mid = (l+r)/2.0;

         if(chk(mid)) r = mid;

         else l = mid;

     }

     if(l > 5e10) puts("-1");

     else printf("%.2lf\n", l);

     return ;

 }