#include <algorithm>
#include <cmath>
#include <climits>
#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <fstream>
#include <iostream>
#include <list>
#include <map>
#include <queue>
#include <set>
#include <sstream>
#include <stack>
#include <string>
#include <vector>
#include <cassert>
#include <functional>

using namespace std;

#define LOG(...) printf(__VA_ARGS__)
//#define LOG(...)
#define FOR(i,a,b) for(int i=(int)(a);i<(int)(b);++i)
#define REP(i,n) for(int i=0;i<(int)(n);++i)
#define ALL(a) (a).begin(),(a).end()
#define RALL(a) (a).rbegin(),(a).rend()
#define EXIST(s,e) ((s).find(e)!=(s).end())
#define SORT(c) sort((c).begin(),(c).end())
#define RSORT(c) sort((c).rbegin(),(c).rend())
#define CLR(a) memset((a), 0 ,sizeof(a))

typedef long long ll;
typedef unsigned long long ull;
typedef vector<bool> vb;
typedef vector<int> vi;
typedef vector<ll> vll;
typedef vector<vb> vvb;
typedef vector<vi> vvi;
typedef vector<vll> vvll;
typedef pair<int, int> pii;
typedef pair<ll, ll> pll;

const int dx[] = {-1,0,1,0}; const int dy[] = {0,1,0,-1};

struct P{
	int p, cost;

	bool operator >(const P& p)const {
		return cost > p.cost;
	}
};

struct Edge{
	int to, cost;
};

const int MAX_TOWN = 21;

int G[MAX_TOWN];

int main() {
	int town_n, road_n, start, goal, money, pay;
	cin >> town_n >> road_n;
	vector<vector<Edge>> E(town_n + 1);

	char gm;
	REP(i, road_n){
		int from, to, costA, costB;
		cin >> from >>gm>> to >>gm>> costA >>gm>> costB;
		E[from].push_back({to, costA});
		E[to].push_back({from, costB});
	}
	cin >> start >>gm>> goal >>gm>> money >>gm>> pay;
	money -= pay;


	{
		fill_n((int * )G, MAX_TOWN, 1e9);
		priority_queue<P, vector<P>, greater<P>> que;
		G[start] = 0;
		que.push({start, 0});

		int res = 0;
		while(!que.empty()){
			P p = que.top(); que.pop();
			if(p.p == goal){
				res = p.cost;
				break;
			}

			for(Edge e:E[p.p]){
				int next_town = e.to;
				int next_cost = p.cost + e.cost;
				if (G[next_town] > next_cost){
					G[next_town] = next_cost;
					que.push({next_town, next_cost});
				}
			}
		}
		money -= res;
	}
	{
		fill_n((int * )G, MAX_TOWN, 1e9);
		priority_queue<P, vector<P>, greater<P>> que;
		G[goal] = 0;
		que.push({goal, 0});

		int res = 0;
		while(!que.empty()){
			P p = que.top(); que.pop();
			if(p.p == start){
				res = p.cost;
				break;
			}

			for(Edge e:E[p.p]){
				int next_town = e.to;
				int next_cost = p.cost + e.cost;
				if (G[next_town] > next_cost){
					G[next_town] = next_cost;
					que.push({next_town, next_cost});
				}
			}
		}
		money -= res;
	}

	cout << money << endl;
}