#pragma comment(linker, "/STACK:1000000000")

 #include <iostream>

 #include <cstdio>

 #include <fstream>

 #include <algorithm>

 #include <cmath>

 #include <deque>

 #include <vector>

 #include <queue>

 #include <string>

 #include <cstring>

 #include <map>

 #include <stack>

 #include <set>

 #define LL long long

 #define INF 0x3f3f3f3f

 #define MAXN 100005

 #define MAXK 100005

 #define eps 1e-8

 using namespace std;

 struct Node{

     double m, now;

 };

 Node p[MAXK];

 int cnt[MAXK];

 vector<int> G[MAXK];

 queue<int> Q;

 int main()

 {

 #ifndef ONLINE_JUDGE

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

     //freopen("out.txt", "w", stdout);

 #endif // OPEN_FILE

     int n, k;

     scanf("%d%d", &n, &k);

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

         scanf("%lf%lf", &p[i].m, &p[i].now);

         //p[i].pos = i;

     }

     int x, y, z;

     //double y;

     memset(cnt, , sizeof(cnt));

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

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

         G[x].push_back(z);

         cnt[z]++;

     }

     scanf("%d%d%d", &x, &y, &z);

    // int head = 1, tail = 1;

     p[x].now += y;

     Q.push(x);

     //vis[x] = true;

     //double ans = p[z].now;

     //int cnt = 0;

     while(!Q.empty()){

         //cnt++;

         int pos = Q.front();

         Q.pop();

         Node q = p[pos];

         if(q.now <= q.m) continue;

         p[pos].now = p[pos].m;

         if(G[pos].size() == ) continue;

         double u =  (q.now - q.m) / G[pos].size();

         for(int i = ; i < G[pos].size(); i++){

             //if(vis[G[q.pos][i]]) continue;

             p[G[pos][i]].now += u;

             //tail++;

             cnt[G[pos][i]]--;

             if(cnt[G[pos][i]] == ){

                 Q.push(G[pos][i]);

             }

         }

     }

     printf("%.6lf\n", p[z].now);

 }