241112-2644.java

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.util.ArrayList;
import java.util.List;
import java.util.StringTokenizer;

public class Main {

    static List<Integer>[] map;
    static boolean[] visited;
    static int answer;

    public static void main(String[] args) throws IOException {
        BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
        int n = Integer.parseInt(br.readLine());
        map = new ArrayList[n + 1];
        visited = new boolean[n + 1];
        for (int i = 1; i <= n; i++) {
            map[i] = new ArrayList<>();
        }
        StringTokenizer st = new StringTokenizer(br.readLine());
        int x = Integer.parseInt(st.nextToken());
        int y = Integer.parseInt(st.nextToken());
        int m = Integer.parseInt(br.readLine());
        for (int i = 0; i < m; i++) {
            st = new StringTokenizer(br.readLine());
            int p = Integer.parseInt(st.nextToken());
            int c = Integer.parseInt(st.nextToken());
            map[p].add(c);
            map[c].add(p);
        }
        answer = -1;
        dfs(x, y, 0);
        System.out.println(answer);
    }

    static void dfs(int start, int end, int cnt) {
        if (start == end) {
            answer = cnt;
            return;
        }

        visited[start] = true;
        for (final int next : map[start]) {
            if (!visited[next]) {
                dfs(next, end, cnt + 1);
            }
        }
    }
}