#include<bits/stdc++.h>
using namespace std;
#define rep(i,n) for (int i = 0; i < (n); ++i)
using ll = long long;
int ctoi(char c){return c-'0';}
ll ctoll(char c){return c-'0';}

const long long INF = 1LL << 60;

//辺を表す型
struct Edge{
     int to; //隣接頂点番号
     long long w; //重み
     Edge(int to, long long w) : to(to), w(w) {}
};

//重み付きグラフを表す型
using Graph = vector<vector<Edge>>;

//緩和を実施する関数
template<class T> bool chmin(T& a, T b){
     if(a > b){
          a = b;
          return true;
     }
     else return false;
}

vector<long long> dijkstra(Graph G, int s){
     int N = G.size();
     //ダイクストラ法
     vector<bool>used(N,false);
     vector<long long>dist(N, INF);
     dist[s] = 0;
     
     priority_queue<pair<long long, int>,vector<pair<long long, int>>, greater<pair<long long, int>>> que;
     que.push(make_pair(dist[s], s));
     
     while(!que.empty()){
          //v:使用済みでない頂点のうち，d[v]が最小の頂点
          //d:vに対するキー値
          int v = que.top().second;
          long long d = que.top().first;
          que.pop();

          if(d > dist[v])continue;

          for(auto e : G[v]){
               if(chmin(dist[e.to],dist[v]+e.w)){
                    que.push(make_pair(dist[e.to], e.to));
               }
          }
     }

     return dist;
}

int main(){
     //長点数, 辺数, 始点
     int N,M;
     cin >> N >> M;
     int s = 0;

     Graph G(N);

     //辺を追加
     for(int i = 0;i < M;i++){
          int a,b;
          cin >> a >> b;
          a--;b--;
          G[a].push_back(Edge(b,1));
     }

     //グラフと始点を渡すと始点からの各頂点への最短距離が帰ってくる
     vector<ll>dist1 = dijkstra(G,0);
     vector<ll>dist2 = dijkstra(G,N-1);
     vector<ll>dist3 = dijkstra(G,N-2);

     ll cost1 = INF;
     ll cost2 = INF;
     ll cost3 = INF;
     ll cost4 = INF;

     cost1 = dist1[N-1] + dist2[N-2] + dist3[0];
     cost2 = dist1[N-2] + dist3[N-1] + dist2[0];
     
     if(dist1[N-1] == dist1[N-2]+dist2[N-2]){
          cost3 = dist1[N-1] + dist2[0];
     }
     if(dist1[N-2] == dist1[N-1]+dist3[N-1]){
          cost4 = dist1[N-2] + dist3[0];
     }

     ll ans = min(cost1,min(cost2,min(cost3,cost4)));
     if(ans == INF)cout << -1 << endl;
     else cout << ans << endl;
}