#include<bits/stdc++.h>
#define int long long
#define rep(i,a,b) for(int i=(a);i<=(b);i++)
#define per(i,a,b) for(int i=(a);i>=(b);i--)
#define fi first
#define se second
#define eb emplace_back
#define popc __builtin_popcount
using namespace std;
typedef long long ll;
typedef pair<int,int> pii;
typedef vector<int> vi;
typedef vector<pii> vp;
typedef unsigned long long ull;
typedef long double ld;

int read() {
    int x=0,w=1; char c=getchar(); 
    while(!isdigit(c)) {if(c=='-') w=-1; c=getchar();}
    while(isdigit(c)) {x=x*10+c-'0'; c=getchar();}
    return x*w;
}

const int N=5e5+9;
int n,fa[N],a[N],sz[N];
ld f[N],g[N],s[N],sum1,sum2,ans;
vi e[N];

void dfs(int u,int x) {
    ld pu=(a[u]+x)%n*1./n;
    sum1+=f[u], sum2+=f[u]*pu;
    for(int v:e[u]) {
        ld pv=(a[v]+x)%n*1./n;
        f[v]=sz[v]*s[u]/pv;
        g[v]=f[v]/sz[v]*(1-pv);
        s[v]=s[u]+g[v];
        dfs(v,x);
    }
}

void work(int r,int p) {
    f[r]=1, g[r]=1./sz[r], s[r]=g[r];
    sum1=0, sum2=0, dfs(r,p);
    ans=max(ans,sum2/sum1);
}

signed main() {
    n=read();
    rep(i,1,n) fa[i]=read(), e[fa[i]].eb(i);
    rep(i,1,n) a[i]=read();
    per(i,n,1) sz[i]++, sz[fa[i]]+=sz[i];
    rep(r,1,n) work(r,n-a[r]);
    printf("%.10Lf\n",ans);
    return 0;
}