#include <bits/stdc++.h>

#define INF 1e9
#define MAX_V 10000

using namespace std;

typedef pair<int,int> ii;
typedef vector<ii> vii;

int n, m, q, s, u, v, w, dist[MAX_V];
vector<vii> adj;

int main() {
    while(scanf("%d%d%d%d",&n,&m,&q,&s),n + m + q + s) {
        adj.assign(n,vii());
        for(int i = 0; i < m; i++) {
            scanf("%d%d%d",&u,&v,&w);
            adj[u].push_back(ii(v,w));
        }
        fill(dist,dist + MAX_V,INF);
        dist[s] = 0;
        priority_queue<ii,vii,greater<ii>> pq;
        pq.push(ii(dist[s],s));
        while(!pq.empty()) {
            ii cur = pq.top(); pq.pop();

            int cur_weight = cur.first;
            int cur_node = cur.second;

            for(auto &x : adj[cur_node]) {
                if(dist[x.first] > cur_weight + x.second) {
                    dist[x.first] = cur_weight + x.second;
                    pq.push(ii(dist[x.first],x.first));
                }
            }
        }
        for(int i = 0; i < q; i++) {
            scanf("%d",&u);
            if(dist[u] == INF) {
                printf("Impossible\n");
            } else {
                printf("%d\n",dist[u]);
            }
        }
        printf("\n");
    }
}