#include <vector>
#include <map>
#include <set>
#include <stack>
#include <queue>
#include <deque>
#include <algorithm>
#include <utility>
#include <functional>
#include <sstream>
#include <iostream>
#include <cstdio>
#include <cmath>
#include <cstdlib>
#include <cctype>
#include <string>
#include <cstring>
#include <ctime>
#include <climits>
using namespace std;
inline int toInt(string s) { int v; istringstream sin(s); sin >> v; return v;}
template<class T> inline string toString(T x) { ostringstream sout; sout << x; return sout.str();}
typedef vector<int> vi;
typedef vector<vi>  vvi;
typedef vector<string> vs;
typedef pair<int, int> pii;
typedef long long ll;
#define ALL(a) (a).begin(),(a).end()
#define RALL(a) (a).rbegin(),(a).rend()
#define FOR(i,a,b) for(int i=(a);i<=(b);++i)
#define REP(i,n) FOR(i,0,(n)-1)
const double EPS = 1e-10;
const double PI = acos(-1.0);
const int INF = INT_MAX/10;

int main() {
	int n, m;
	cin >> n >> m;

	vvi cost(n, vi(n, INF));
	int a, b, d, e;
	char c;
	REP(i, m) {
		cin >> a >> c >> b >> c >> d >> c >> e;
		cost[a-1][b-1] = d;
		cost[b-1][a-1] = e;
	}
	cin >> a >> c >> b >> c >> d >> c >> e;

	REP(k, n) {
		REP(i, n) {
			REP(j, n) {
				cost[i][j] = min(cost[i][j], cost[i][k]+cost[k][j]);
			}
		}
	}

	cout << d-e-cost[a-1][b-1]-cost[b-1][a-1] << endl;
    return 0;
}