import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.HashMap;
import java.util.HashSet;
import java.util.LinkedList;
import java.util.Map;
import java.util.Queue;

public class Main {

  static Map<Integer, ArrayList<Integer>> graph = new HashMap<>();
  static HashSet<Integer> visited = new HashSet<>();
  static int[] location;

  public static int bfs(int start, int target) {
    Queue<Integer> queue = new LinkedList<>();
    queue.add(start);
    visited.add(start);

    while (!queue.isEmpty()) {
      Integer poll = queue.poll();
      for (int neighbor : graph.get(poll)) {
        if (!visited.contains(neighbor)) {
          queue.add(neighbor);
          visited.add(neighbor);
          location[neighbor] = location[poll] + 1;
          if (neighbor == target) {
            return location[neighbor];
          }
        }
      }
    }
    return -1;
  }


  public static void main(String[] args) throws IOException {
    BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
    int vertex = Integer.parseInt(br.readLine());
    int[] compare = Arrays.stream(br.readLine().split(" ")).mapToInt(Integer::parseInt).toArray();
    int count = Integer.parseInt(br.readLine());

    for (int i = 0; i < count; i++) {
      int[] edges = Arrays.stream(br.readLine().split(" ")).mapToInt(Integer::parseInt).toArray();
      graph.putIfAbsent(edges[0], new ArrayList<>());
      graph.putIfAbsent(edges[1], new ArrayList<>());
      graph.get(edges[0]).add(edges[1]);
      graph.get(edges[1]).add(edges[0]);
    }

    location = new int[vertex + 1];
    System.out.println(bfs(compare[0], compare[1]));
  }