#include <iostream>
#include <algorithm>
#include <map>
#include <set>
#include <queue>
#include <stack>
#include <numeric>
#include <bitset>
#include <cmath>

static const int MOD = 1000000007;
using ll = long long;
using u32 = unsigned;
using u64 = unsigned long long;
using namespace std;

template<class T> constexpr T INF = ::numeric_limits<T>::max()/32*15+208;

template <typename T>
struct edge {
    int from, to; T cost;
    edge(int to, T cost) : from(-1), to(to), cost(cost) {}
    edge(int from, int to, T cost) : from(from), to(to), cost(cost) {}
};

template <class K, class V>
class RadixHeap {
    static constexpr int bit_length = sizeof(K)*8;
    K last;
    size_t sz, cnt;

    array<vector<pair<K, V>>, bit_length> v;
    static inline int bsr(int x){
        return x ? bit_length-__builtin_clz(x) : 0;
    }
    static inline int bsr(ll x){
        return x ? bit_length-__builtin_clzll(x) : 0;
    }

    void pull() {
        if(cnt < v[0].size()) return;;
        int i = 1;
        while(v[i].empty()) i++;
        last = min_element(v[i].begin(),v[i].end())->first;
        for (auto &&x : v[i]) v[bsr(x.first ^ last)].push_back(x);
        v[i].clear();
    }
public:
    RadixHeap() : last(0), sz(0), cnt(0) {}
    void emplace(K x, V val){
        sz++;
        v[bsr(x^last)].emplace_back(x, val);
    }

    pair<K, V> top() {
        pull();
        return v[0][cnt];
    }

    void pop() {
        pull();
        sz--;
        cnt++;
    }

    size_t size() const { return sz; }
    bool empty() const { return !sz; }
};
template <typename T>
vector<T> dijkstra(int s,vector<vector<edge<T>>> &G){
    auto n = G.size();
    vector<T> d(n, INF<T>);
    RadixHeap<T, int> Q;
    d[s] = 0;
    Q.emplace(0, s);
    while(!Q.empty()){
        T cost; int i;
        tie(cost, i) = Q.top(); Q.pop();
        if(d[i] < cost) continue;
        for (auto &&e : G[i]) {
            auto cost2 = cost + e.cost;
            if(d[e.to] <= cost2) continue;
            d[e.to] = cost2;
            Q.emplace(d[e.to], e.to);
        }
    }
    return d;
}

int main() {
    int n, m;
    cin >> n >> m;
    vector<vector<edge<int>>> G(n);
    for (int i = 0; i < m; ++i) {
        int a, b, c, d;
        scanf("%d,%d,%d,%d", &a, &b, &c, &d);
        a--; b--;
        G[a].emplace_back(b, c);
        G[b].emplace_back(a, d);
    }
    int s, g, v, p;
    scanf("%d,%d,%d,%d", &s, &g, &v, &p);
    s--; g--;
    cout << v-p-dijkstra(s, G)[g]-dijkstra(g, G)[s] << "\n";
    return 0;
}
