import java.io.;
import java.math.;
import java.security.;
import java.text.;
import java.util.;
import java.util.concurrent.;
import java.util.regex.*;
public class Solution {
// Complete the findShortest function below.
/*
* For the unweighted graph, <name>:
*
* 1. The number of nodes is <name>Nodes.
* 2. The number of edges is <name>Edges.
* 3. An edge exists between <name>From[i] to <name>To[i].
*
*/
static int findShortest(int graphNodes, int[] graphFrom, int[] graphTo, long[] ids, int val) {
// solve here
ArrayList<ArrayList<Integer>> al = new ArrayList<>();
for(int i=0;i<graphNodes;i++)
{
al.add(new ArrayList<Integer>());
}
for(int i=0;i<graphFrom.length;i++)
{
al.get(graphFrom[i]-1).add(graphTo[i]-1);
al.get(graphTo[i]-1).add(graphFrom[i]-1);
}
boolean[] visited = new boolean[graphNodes];
int start =0;
for(int i=0;i<ids.length;i++)
{
if(val==ids[i])
{
start =i;
break;
}
}
Queue<Integer> q = new LinkedList<>();
q.add(start);
visited[start]= true;
int[] dist = new int[graphNodes];
while(!q.isEmpty())
{
int u = q.poll();
for(int v : al.get(u))
{
if(visited[v]==false)
{
visited[v]=true;
q.add(v);
dist[v] = dist[u]+1;
}
}
}
int min = Integer.MAX_VALUE;
for(int i=start+1;i<graphNodes;i++)
{
if(val == ids[i])
{
min = Math.min(min,dist[i]);
}
}
if(min==Integer.MAX_VALUE)
{
return -1;
}
else
{
return min;
}
}
private static final Scanner scanner = new Scanner(System.in);
public static void main(String[] args) throws IOException {
BufferedWriter bufferedWriter = new BufferedWriter(new FileWriter(System.getenv("OUTPUT_PATH")));
String[] graphNodesEdges = scanner.nextLine().split(" ");
int graphNodes = Integer.parseInt(graphNodesEdges[0].trim());
int graphEdges = Integer.parseInt(graphNodesEdges[1].trim());
int[] graphFrom = new int[graphEdges];
int[] graphTo = new int[graphEdges];
for (int i = 0; i < graphEdges; i++) {
String[] graphFromTo = scanner.nextLine().split(" ");
graphFrom[i] = Integer.parseInt(graphFromTo[0].trim());
graphTo[i] = Integer.parseInt(graphFromTo[1].trim());
}
long[] ids = new long[graphNodes];
String[] idsItems = scanner.nextLine().split(" ");
scanner.skip("(\r\n|[\n\r\u2028\u2029\u0085])?");
for (int i = 0; i < graphNodes; i++) {
long idsItem = Long.parseLong(idsItems[i]);
ids[i] = idsItem;
}
int val = scanner.nextInt();
scanner.skip("(\r\n|[\n\r\u2028\u2029\u0085])?");
int ans = findShortest(graphNodes, graphFrom, graphTo, ids, val);
bufferedWriter.write(String.valueOf(ans));
bufferedWriter.newLine();
bufferedWriter.close();
scanner.close();
}
}