#include<bits/stdc++.h>

using namespace std;

#define eps 1e-9

#define bug(x) cout<<#x<<'='<<x<<endl;

#define Min 1e-7

const int maxn = 1e4+;

const int maxe = 1e5+;

struct Ponds

{

    double cap,now;

};

typedef Ponds Pants;

Pants P[maxn];

int N,K;

vector<int> son[maxn];

int St,Tar,Amount;

int in[maxn];

queue<int> q;

void topo()

{

    P[St].now += Amount;

    q.push(St);

    for(int i = ; i <= N; i++) if(!in[i] && i!= St) q.push(i);

    while(q.size()){

        int u = q.front(); q.pop();

        Pants &p = P[u];

        if(p.now - p.cap > ){

            if(son[u].size()){

                double each = (p.now-p.cap)/son[u].size();

                 p.now = p.cap;

                for(int i = ; i < son[u].size(); i++){

                    int v = son[u][i];

                    P[v].now += each;

                    if(--in[v] ==  ) q.push(v);

                }

            }else {

                p.now = p.cap;

            }

        }

    }

}

int main()

{

    //freopen("in.txt","r",stdin);

    scanf("%d%d",&N,&K);

    for(int i = ; i <= N; i++){

        scanf("%lf%lf",&P[i].cap,&P[i].now);

    }

    for(int i = ; i < K; i++){

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

        son[u].push_back(v);

        in[v]++;

    }

    scanf("%d%d%d",&St,&Amount,&Tar);

    topo();

    printf("%lf",P[Tar].now);

    return ;

}