#include<cstdio>

#include<cstring>

#include<cmath>

#include<vector>

#include<map>

#include<stack>

#include<queue>

#include<string>

#include<iostream>

#include<algorithm>

using namespace std;

const int maxn=+;

vector<int>tree[maxn];

int n;

double P,r;

double sum;

int sz;

int num[maxn];

void dfs(int x,double price)

{

    if(tree[x].size()==)

    {

        sum=sum+num[x]*price;

        sz++;

        return;

    }

    for(int i=;i<tree[x].size();i++)

        dfs(tree[x][i],price*(+r/)*1.0);

}

int main()

{

    scanf("%d",&n);

    scanf("%lf%lf",&P,&r);

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

    {

        int ki; scanf("%d",&ki);

        if(ki==)

        {

            int x; scanf("%d",&x);

            num[i]=x;

        }

        else

        {

            while(ki--)

            {

                int to; scanf("%d",&to);

                tree[i].push_back(to);

            }

        }

    }

    sum=;sz=;

    dfs(,P);

    printf("%.1lf\n",sum);

    return ;

}