#include<iostream>
#include<string.h>
#include<algorithm>
#include<math.h>
#include<vector>
#include<map>
#include<queue>
#include<set> 
#include<stack>
#include<bitset>
#include<unordered_map>
#include<iomanip>
#define endl '\n'
#define pb push_back
#define debug(x) cout<<x<<endl; 
#define me(a,x) memset(a,x,sizeof(a))
#define L(i,j,k) for(int i=(j);i<=(k);++i)
#define R(i,j,k) for(int i=(j);i>=(k);--i)
#define int long long 
using namespace std;
typedef long long ll;
typedef pair<int ,int > PII;
typedef unsigned long long ull;
int n,m;
vector<int> v[110];
int a[110],b[110],st[110];
struct node{
	int a,b,c;
	friend bool operator<(node a,node b){
		if(a.c==b.c)return a.a>b.a;
		return a.c>b.c;
	}
}t[110];
int bfs(int u){
	priority_queue<node> q;
	q.push({0,u,0});
	int res=0;
	while(!q.empty()){
		int u=q.top().b;
		q.pop();
		if(st[u])continue;
		st[u]=1;
		for(int i=0;i<v[u].size();i++){
			int j=v[u][i];
			res+=b[j]-a[j];
			q.push({a[j],j,b[j]-a[j]});
		}
	}
	return res;
}
signed main(){
	ios::sync_with_stdio(false);cin.tie(0);cout.tie(0);
	cin>>n>>m;
	L(i,2,n){
		cin>>a[i]>>b[i];
	}
	L(i,1,m){
		int x,y;cin>>x>>y;
		v[x].pb(y);
	}
	cout<<bfs(1);
}