//#define _GLIBCXX_DEBUG
#include <bits/stdc++.h>
#include <atcoder/modint>
#include <atcoder/dsu>
#include <boost/rational.hpp>
using namespace std;
using namespace atcoder;
using ll = long long;
using mint = modint998244353;
const double pi = 3.14159265359879323846264338327950288419;
const ll INF = 9 * 1e6;
using p = pair<ll, ll>;

int main() {
  int n, m; cin >> n >> m;
  map<int, vector<int>> mp;
  for(int i = 0; i < m; i++){
    int U, V; cin >> U >> V;
    mp[U-1].push_back(V-1);
  }
  vector<ll> dis_from_0(n, INF);
  dis_from_0[0] = 0;
  queue<int> q;
  q.push(0);
  while(!q.empty()){
    int v = q.front(); q.pop();
    for(auto nv : mp[v]){
      if(dis_from_0[nv] != INF) continue;
      dis_from_0[nv] = dis_from_0[v] + 1;
      q.push(nv);
    }
  }
  
  vector<ll> dis_from_n(n, INF);
  dis_from_n[n-1] = 0;
  q.push(n-1);
  while(!q.empty()){
    int v = q.front(); q.pop();
    for(auto nv : mp[v]){
      if(dis_from_n[nv] != INF) continue;
      dis_from_n[nv] = dis_from_n[v] + 1;
      q.push(nv);
    }
  }
  
  vector<ll> dis_from_n1(n, INF);
  dis_from_n1[n-2] = 0;
  q.push(n-2);
  while(!q.empty()){
    int v = q.front(); q.pop();
    for(auto nv : mp[v]){
      if(dis_from_n1[nv] != INF) continue;
      dis_from_n1[nv] = dis_from_n1[v] + 1;
      q.push(nv);
    }
  }
  
  //for(auto c : dis_from_n1) cerr << c << " ";
  ll zero_n_n1 = dis_from_0[n-1] + dis_from_n[n-2] + dis_from_n1[0],
     zero_n1_n = dis_from_0[n-2] + dis_from_n1[n-1] + dis_from_n[0];
  
  cout << (min(zero_n_n1, zero_n1_n) >= INF ? -1:min(zero_n_n1, zero_n1_n)) << endl;
}