import java.util.*;

public class Main{
    static int N = 100010;
    static int[] q = new int[N];
    static int[] d = new int[N];
    static int[] e = new int[N];
    static int[] ne = new int[N];
    static int[] h = new int[N];
    static int idx;
    static void add(int a,int b){
        e[idx] = b;
        ne[idx] = h[a];
        h[a] = idx++;
    }
    public static void main(String[] args){
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        int m = sc.nextInt();
        for(int i=0;i<N;i++){
            h[i]=-1;
        }
        while(m-->0){
            int a = sc.nextInt();
            int b = sc.nextInt();
            add(a,b);
        }
        for(int i=0;i<N;i++){
            d[i]=-1;
        }
        int hh=0,tt=0;
        q[0] = 1;d[1]=0;
        while(hh<=tt){
            int t = q[hh++];
            for(int i=h[t];i!=-1;i=ne[i]){
                int j = e[i];
                if(d[j]==-1){
                    d[j] = d[t]+1;
                    q[++tt] = j;
                }
            }
        }
       System.out.print(d[n]);
    }
}