#include<bits/stdc++.h>
namespace {
#pragma GCC diagnostic ignored "-Wunused-function"
#include<atcoder/all>
#pragma GCC diagnostic warning "-Wunused-function"
using namespace std;
using namespace atcoder;
#define rep(i,n) for(int i = 0; i < (int)(n); i++)
#define rrep(i,n) for(int i = (int)(n) - 1; i >= 0; i--)
#define all(x) begin(x), end(x)
#define rall(x) rbegin(x), rend(x)
template<class T> bool chmax(T& a, const T& b) { if (a < b) { a = b; return true; } else return false; }
template<class T> bool chmin(T& a, const T& b) { if (b < a) { a = b; return true; } else return false; }
using ll = long long;
using P = pair<int,int>;
using VI = vector<int>;
using VVI = vector<VI>;
using VL = vector<ll>;
using VVL = vector<VL>;

constexpr int INF = 1001001001;
template <int k = 2, class T>  // cost in [0, k)
vector<int> kBFS(const vector<vector<pair<int, T>>>& g, int s = 0) {
  static_assert(k >= 1);
  const int n = g.size();
  vector<int> dist(n, INF);
  vector<int> q[2 * k];
  dist[s] = 0;
  q[0].emplace_back(s);
  for (int dist_cur = 0, ptr = 0;;) {
    const auto qb = q + ptr;
    while (!qb[0].empty()) {
      int u = qb[0].back();
      qb[0].pop_back();
      if (dist[u] != dist_cur) continue;
      for (auto [v, c] : g[u]) {
        int nd = dist_cur + c;
        if (nd < dist[v]) {
          dist[v] = nd;
          qb[c].emplace_back(v);
        }
      }
    }
    do {
      dist_cur++;
      ptr++;
      if (ptr == 2 * k) return dist;
    } while (q[ptr].empty());
    if (ptr > k) {
      for (int i = ptr; i < 2 * k; i++) {
        swap(q[i], q[i - ptr]);
      }
      ptr = 0;
    }
  }
}

} int main() {
  ios::sync_with_stdio(false);
  cin.tie(0);
  int n, m;
  cin >> n >> m;
  vector<vector<P>> to(4 * n);
  rep(_, m) {
    int u, v;
    cin >> u >> v;
    u--, v--;
    rep(s, 4) to[n * s + u].emplace_back(n * s + v, 1);
  }
  rep(s0, 2) to[n * s0 + n - 2].emplace_back(n * (s0 + 2) + n - 2, 0);
  rep(s1, 2) to[n * (2 * s1) + n - 1].emplace_back(n * (2 * s1 + 1) + n - 1, 0);
  int ans = kBFS(to)[3 * n];
  if (ans == INF) ans = -1;
  cout << ans << '\n';
}