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.LinkedList;
import java.util.Map;
import java.util.Queue;
import java.util.TreeSet;

public class Main {

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

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

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

    visited = new int[split[0] + 1];
    Arrays.fill(visited, -1);
    bfs(split[3], split[2]);
    TreeSet<Integer> set = new TreeSet<>();
    for (int i = 1; i < visited.length; i++) {
      if (visited[i] == split[2]) {
        set.add(i);
      }
    }

    if (set.isEmpty()) {
      System.out.println(-1);
    } else {
      for (Integer integer : set) {
        System.out.println(integer);
      }
    }
  }

  public static void bfs(int start, int min) {
    Queue<Integer> queue = new LinkedList<>();
    queue.add(start);
    visited[start] = 0;

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

}