import java.util.*;
class Main {
    Scanner sc = new Scanner(System.in);
    int n, m;
    int N = 100005;
    List<Integer>[] g = new List[N];
    int[] dist = new int[N];

    void run() {
        n = sc.nextInt(); m = sc.nextInt();
        for (int i = 0; i < n; i++) {
            g[i] = new ArrayList<>();
        }
        for (int i = 0; i < m; i++) {
            int a = sc.nextInt() - 1, b = sc.nextInt() - 1;
            if (a == b) continue;
            g[a].add(b);
        }
        Queue<Integer> queue = new LinkedList<>();
        Arrays.fill(dist, -1);
        dist[0] = 0;
        queue.add(0);
        while (!queue.isEmpty()) {
            int u = queue.poll();
            for (int v : g[u]) {
                if (dist[v] != -1) continue;
                dist[v] = dist[u] + 1;
                if (v == n - 1) {
                    System.out.println(dist[v]);
                    return;
                }
                queue.add(v);
            }
        }
        System.out.println(-1);
    }
    public static void main(String[] args) {
        Main m = new Main();
        m.run();
    }
}