#include<iostream>

#include<cstring>

#include<algorithm>

#include<cstdio>

#define Maxn 1010

using namespace std;

int sum[Maxn],worm[Maxn],le[Maxn],vi[Maxn],head[Maxn],e,n,back[Maxn];

struct Edge{

    int u,v,next;

}edge[Maxn*Maxn];

void init()

{

    memset(sum,,sizeof(sum));

    memset(worm,,sizeof(worm));

    memset(le,,sizeof(le));

    memset(vi,,sizeof(vi));

    memset(back,,sizeof(back));

    memset(head,-,sizeof(head));

    e=;

}

void add(int u,int v)

{

    edge[e].u=u,edge[e].v=v,edge[e].next=head[u],head[u]=e++;

}

int cmp(int a,int b)

{

    return (back[a]+)*le[b]<(back[b]+)*le[a];

}

void dfs(int u)

{

    int i,v,cnt;

    int use[];

    cnt=;

    if(head[u]==-)

    {

        le[u]=;

        return ;

    }

    for(i=head[u];i!=-;i=edge[i].next)

    {

        v=edge[i].v;

        dfs(v);

        use[++cnt]=v;

        le[u]+=le[v];

    }

    sort(use+,use++cnt,cmp);

    for(i=;i<=cnt;i++)

    {

        sum[u]+=(back[u]+)*le[use[i]]+sum[use[i]];

        back[u]+=back[use[i]]+;

    }

    if(worm[u])

        back[u]=;

}

int main()

{

    int i,j,a;

    char str[];

    while(scanf("%d",&n),n)

    {

        init();

        scanf("%d%s",&a,&str);

        if(str[]=='Y')

            worm[]=;

        for(i=;i<=n;i++)

        {

            scanf("%d%s",&a,&str);

            add(a,i);

            if(str[]=='Y')

                worm[i]=;

        }

        dfs();

        double temp=sum[];

        printf("%.4lf\n",sum[]/(1.0*le[]));

    }

    return ;

}