C++代码：

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

typedef pair<int, int> node;
const int N = 1010, M = N * N;
int h[N], d[N], cd[N], e[M], ne[M], w[M], v[M], idx;
int q[N];
int dist[N], sum[N], pre[N];
bool st[N];
int n, m, k;

void add(int a, int b, int p, int q)
{
    e[idx] = b, w[idx] = p, v[idx] = q, ne[idx] = h[a], h[a] = idx++;
}

// 判断有向图是否有环
bool topsort() 
{
    int hh = 0, tt = -1;
    for (int i = 0; i < n; i++) if (!d[i]) q[++tt] = i;

    while (hh <= tt) 
    {
        int t = q[hh++];

        for (int i = h[t]; ~i; i = ne[i])
        {
            int j = e[i];
            d[j]--;
            if (!d[j]) q[++tt] = j;
        }
    }

    if (tt == n - 1) return false;
    return true;
}

void dijkstra()
{
    memset(dist, 0x3f, sizeof dist);
    dist[n] = 0, pre[n] = -1;
    priority_queue<node, vector<node>, greater<node>> heap;

    heap.push({ 0, n });

    while (!heap.empty())
    {
        auto head = heap.top();
        heap.pop();
        int distance = head.first, t = head.second;

        if (st[t]) continue;
        st[t] = true;

        for (int i = h[t]; ~i; i = ne[i])
        {
            int j = e[i];
            if (dist[j] > distance + w[i])
            {
                dist[j] = distance + w[i];
                sum[j] = sum[t] + v[i];
                pre[j] = t;
                heap.push({ dist[j], j });
            }
            else if (dist[j] == distance + w[i] && sum[j] < sum[t] + v[i])
            {
                sum[j] = sum[t] + v[i];
                pre[j] = t;
            }
        }
    }
}

int main()
{
    scanf("%d%d", &n, &m);
    memset(h, -1, sizeof h);

    while (m--)
    {
        int a, b, p, q;
        scanf("%d%d%d%d", &a, &b, &p, &q);
        add(a, b, p, q);
        d[b]++;
    }

    // 做完拓扑排序, d已经被清空
    memcpy(cd, d, sizeof d);

    bool circle = topsort();
    if (circle) puts("Impossible.");
    else
    {
        puts("Okay.");

        // 建立虚拟源点
        for (int i = 0; i < n; i++)
            if (!cd[i]) add(n, i, 0, 0);

        dijkstra();
    }

    scanf("%d", &k);
    while (k--)
    {
        int x;
        scanf("%d", &x);
        if (circle)
        {
            if (!cd[x]) printf("You may take test %d directly.\n", x);
            else puts("Error.");
        }
        else
        {
            if (!cd[x]) printf("You may take test %d directly.\n", x);
            else
            {
                vector<int> path;
                for (int i = x; ~pre[i]; i = pre[i]) path.push_back(i);

                reverse(path.begin(), path.end());
                printf("%d", path[0]);
                for (int i = 1; i < path.size(); i++) printf("->%d", path[i]);
                puts("");
            }
        }
    }

    return 0;
}