#include <stdio.h>
#define maxn 0x3f3f3f3f

int map[1005][1005], dis[1005], visited[1005];

void Dijkstra(int start, int n)     //最短路的模板
{
    int mind;
    int pre = start;
    for(int i = 1; i<=n; i++)
    {
        dis[i] = map[start][i];
        visited[i] = 0;
    }
    visited[start] = 1;
    for(int i = 1; i<=n; i++)
    {
        mind = maxn;
        for(int j = 1; j<=n; j++)
        {
            if(mind > dis[j] && !visited[j])
            {
                mind = dis[j];
                pre = j;
            }
        }
        visited[pre] = 1;
        for(int j = 1; j<=n; j++)
        {
            if(dis[j] > dis[pre]+map[pre][j] && !visited[j])
                dis[j] = dis[pre]+map[pre][j];
        }
    }
}

int main()
{
    int n, m, k, start, finish;
    int x, y, vaule, mind;
    while(scanf("%d%d%d", &n, &m, &finish)!=EOF)
    {
        for(int i = 1; i<=n; i++)     //进行初始化
        {
            for(int j = 1; j<=n; j++)
            {
                    map[i][j] = maxn;
            }
        }

        while(m--)
        {
            scanf("%d%d%d", &x, &y, &vaule);
            if(map[y][x] > vaule)
            {
                map[y][x] = vaule;           //改变他们的指向，为后面做好准备，并要最短的那一条路
            }

        }
        mind = maxn;
        scanf("%d", &k);
        Dijkstra(finish, n);           //查找终点到各个点的距离
        for(int i = 1; i<=k; i++)
        {
            scanf("%d", &start);
            if( mind > dis[start])
                mind = dis[start];
        }
        if(mind != maxn)
            printf("%d\n", mind);
        else
            printf("-1\n");
    }

    return 0;
}