#include <bits/stdc++.h>
#include <atcoder/all>
using namespace std;
using namespace atcoder;
using ll = long long;
using ld = long double;
using mint = modint998244353;

const ll INF = 1LL << 60;

vector<ll> bfs(int start, vector<vector<int>> &graph, int N) {
  vector<ll> dists(N, INF);
  dists[start] = 0;

  queue<pair<int, ll>> q;
  q.push({start, 0});
  while (!q.empty()) {
    auto [u, d] = q.front(); q.pop();
    for (int v: graph[u]) {
      if (dists[v] < INF) continue;
      dists[v] = d + 1;
      q.push({v, dists[v]});
    }
  }
  return dists;
} 

int main() {
  int N, M; cin >> N >> M;
  vector<vector<int>> graph(N);
  for (int i = 0; i < M; i++) {
    int u, v; cin >> u >> v;
    u--, v--;
    graph[u].push_back(v);
  }
  vector<ll> dists_0 = bfs(0, graph, N);
  vector<ll> dists_N_2 = bfs(N - 2, graph, N);
  vector<ll> dists_N_1 = bfs(N - 1, graph, N);

  ll ans1 = dists_0[N - 2] + dists_N_2[N - 1] + dists_N_1[0];
  ll ans2 = dists_0[N - 1] + dists_N_1[N - 2] + dists_N_2[0];
  ll ans = min(ans1, ans2); 
  cout << (ans >= INF ? -1: ans) << endl;
  return 0;
}