import java.util.*;
import java.io.*;
class Main{
	private static final BufferedReader br =
		new BufferedReader(new InputStreamReader(System.in));
	private static final PrintWriter out =
		new PrintWriter(System.out);
	public static void main(String[] args)throws IOException{

		String[] str = br.readLine().split(" ");
		int N = Integer.parseInt(str[0]);
		int M = Integer.parseInt(str[1]);
		ArrayList<ArrayList<Integer>> list = new ArrayList<>();
		for(int i=0;i<=N;i++)
			list.add(new ArrayList<>());
		while(M-->0){
			str = br.readLine().split(" ");
			int u = Integer.parseInt(str[0]);
			int v = Integer.parseInt(str[1]);
			list.get(u).add(v);
		}
		PriorityQueue<int[]> queue = new PriorityQueue<>((a,b)->Integer.compare(a[1],b[1]));
		int[] dist = new int[4*N+1];
		Arrays.fill(dist,Integer.MAX_VALUE);
		dist[1] = 0;
		queue.add(new int[]{1,0,0});
		while(queue.size()>0){
			int[] now = queue.poll();
			if(dist[now[0]+now[2]*N]<now[1])
				continue;
			for(int next:list.get(now[0])){
				int nextP = next==N-1?now[2]|1:next==N?now[2]|2:now[2];
				if(dist[now[0]+now[2]*N]+1<dist[next+nextP*N]){
					dist[next+nextP*N] = dist[now[0]+now[2]*N]+1;
					queue.add(new int[]{next,dist[next+nextP*N],nextP});
				}
			}
		}
		out.println(dist[3*N+1]==Integer.MAX_VALUE?-1:dist[3*N+1]);

		br.close();
		out.close();
	}
}