using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

namespace ConsoleApplication1
{
    class Node
    {
        internal List<Edge> routes;

        public Node()
        {
            routes = new List<Edge>();
        }
    }

    class Edge : IComparable
    {
        internal int target;
        internal int cost;

        public Edge(int target, int cost)
        {
            this.target = target;
            this.cost = cost;
        }

        public int CompareTo(object obj)
        {
            Edge temp = obj as Edge;
            return temp.cost - cost;    // Reverse
        }
    }

    class Program
    {
        static void Main(string[] args)
        {
            int n = int.Parse(Console.ReadLine());
            int m = int.Parse(Console.ReadLine());

            Node[] nodeList = new Node[n + 1];
            for (int i = 0; i <= n; i++) nodeList[i] = new Node();

            string[] input;

            for (int i = 0; i < m; i++)
            {
                input = Console.ReadLine().Split(',');
                int a = int.Parse(input[0]);
                int b = int.Parse(input[1]);
                int c = int.Parse(input[2]);
                int d = int.Parse(input[3]);

                nodeList[a].routes.Add(new Edge(b, c));
                nodeList[b].routes.Add(new Edge(a, d));
            }

            input = Console.ReadLine().Split(',');
            int s = int.Parse(input[0]);
            int g = int.Parse(input[1]);
            int V = int.Parse(input[2]);
            int P = int.Parse(input[3]);

            int forward = Dijkstra(nodeList, s, g);
            int backward = Dijkstra(nodeList, g, s);

            Console.WriteLine(V - P - forward - backward);
        }

        static int Dijkstra(Node[] nodeList, int start, int target)
        {
            PriorityQueue<Edge> pq = new PriorityQueue<Edge>();

            int n = nodeList.Length;

            int[] costs = Enumerable.Repeat(int.MaxValue, n).ToArray();
            bool[] visited = new bool[n];

            costs[start] = 0;
            pq.Enqueue(new Edge(start, 0));

            while (pq.Count() > 0)
            {
                Edge f = pq.Dequeue();
                int u = f.target;
                visited[u] = true;

                if (costs[u] < f.cost) continue;

                for (int j = 0; j < nodeList[u].routes.Count; j++)
                {
                    int v = nodeList[u].routes[j].target;

                    if (visited[v] == true) continue;

                    if (costs[v] > costs[u] + nodeList[u].routes[j].cost)
                    {
                        costs[v] = costs[u] + nodeList[u].routes[j].cost;
                        pq.Enqueue(new Edge(v, costs[v]));
                    }
                }
            }
            return costs[target];
        }
    }

    class PriorityQueue<T> where T : IComparable
    {
        List<T> heap;
        int size;

        public PriorityQueue()
        {
            heap = new List<T>();
        }

        public void Enqueue(T x)
        {
            heap.Add(x);
            int i = size++;

            while (i > 0)
            {
                int p = (i - 1) / 2;

                if (Compare(heap[p], x) <= 0) break;

                heap[i] = heap[p];
                i = p;
            }
            heap[i] = x;
        }

        public T Dequeue()
        {
            T ret = heap[0];
            T x = heap[--size];

            int i = 0;
            while (i * 2 + 1 < size)
            {
                int a = i * 2 + 1;
                int b = i * 2 + 2;

                if (b < size && Compare(heap[b], heap[a]) < 0)
                    a = b;
                if (Compare(heap[a], x) >= 0)
                    break;

                heap[i] = heap[a];
                i = a;
            }
            heap[i] = x;
            heap.RemoveAt(size);
            return ret;
        }

        public int Count()
        {
            return size;
        }

        private int Compare(T x, T y)
        {
            return y.CompareTo(x);
        }
    }
}

Measured memory_bytes: 9560