#include <iostream>
#include <cstdio>
#include <vector>
#include <algorithm>
#include <complex>
#include <cstring>
#include <cstdlib>
#include <queue>
using namespace std;

#define REP(i,n) for(int i=0;i<(int)n;++i)
#define FOR(i,c) for(__typeof((c).begin())i=(c).begin();i!=(c).end();++i)
#define ALL(c) (c).begin(), (c).end()
#define INF 1<<30

typedef int Weight;
struct Edge {
  int src, dst;
  Weight weight;
  Edge(int src, int dst, Weight weight) :
    src(src), dst(dst), weight(weight) { }
};

bool operator < (const Edge &e, const Edge &f) {
  return e.weight != f.weight ? e.weight > f.weight : // !!INVERSE!!
    e.src != f.src ? e.src < f.src : e.dst < f.dst;
}

typedef vector<Edge> Edges;
typedef vector<Edges> Graph;

void shortestPath(const Graph &g, int s, vector<Weight> &dist) {
  int n = g.size();
  dist.assign(n, INF); dist[s] = 0;
  priority_queue<Edge> Q; // "e < f" <=> "e.weight > f.weight"
  for (Q.push(Edge(-2, s, 0)); !Q.empty(); ) {
    Edge e = Q.top(); Q.pop();
    if (dist[e.dst] < e.weight) continue;
    FOR(f,g[e.dst]) {
      if (dist[f->dst] > e.weight+f->weight) {
        dist[f->dst] = e.weight+f->weight;
        Q.push(Edge(f->src, f->dst, e.weight+f->weight));
      }
    }
  }
}

int main() {
  int n,m;
  cin >> n >> m;
  Graph g(n);
  REP(i,m) {
    int a,b,c,d;
    scanf("%d,%d,%d,%d\n",&a,&b,&c,&d);
    a--;b--;
    g[a].push_back(Edge(a,b,c));
    g[b].push_back(Edge(b,a,d));
  }
  int s, d, y1, y2;
  scanf("%d,%d,%d,%d\n",&s,&d,&y1,&y2);
  s--;d--;
  vector<int> dist;
  int hoge;
  shortestPath(g, s, dist);
  hoge = dist[d];
  shortestPath(g,d,dist);
  hoge += dist[s];
  cout << y1 - y2 - hoge << endl;
}