#include <bits/stdc++.h>
#include<stdio.h>
using namespace std;
#define FOR(i,k,n) for(int i = (k); i < (n); i++)
#define REP(i,n) FOR(i,0,n)
#define ALL(a) begin(a),end(a)
#define MS(m,v) memset(m,v,sizeof(m))
#define D10  fixed<<setprecision(10)
typedef vector<int> vi;
typedef vector<string> vs;
typedef pair<int, int> P;
typedef long long ll;
const ll INF = 114514810;
const ll MOD = 1000000007;
const double EPS = 1e-8;
const double PI = acos(-1.0);
struct edge
{
	int from, to, cost;
	bool operator < (const edge& e) const { return cost < e.cost; }
	bool operator >(const edge& e) const { return cost > e.cost; }
};
int dx[] = { -1, 0, 0, 1 }; int dy[] = { 0, -1, 1, 0 };
bool valid(int x, int y, int h, int w) { return (x >= 0 && y >= 0 && x < h&&y < w); }
///*************************************************************************************///
///*************************************************************************************///
///*************************************************************************************///

int main()
{
	int n, m;
	cin >> n >> m;
	int g[30][30];
	REP(i, n)REP(j, n) g[i][j] = (i == j ? 0 : INF);
	REP(i, m)
	{
		int a, b, c, d;
		scanf("%d,%d,%d,%d", &a, &b, &c, &d);
		a--; b--;
		g[a][b] = c;
		g[b][a] = d;
	}
	REP(k, n)REP(i, n)REP(j, n) g[i][j] = min(g[i][j], g[i][k] + g[k][j]);
	int a, b, c, d; 
	scanf("%d,%d,%d,%d", &a, &b, &c, &d);
	a--; b--;
	cout << c - d - g[a][b] - g[b][a] << endl;
	return 0;
}