#include <iostream>
#include <iomanip>
#include <vector>
#include <algorithm>
#include <utility>
#include <string>
#include <queue>
#include <stack>
#include <deque>
#include <unordered_set>
#include <unordered_map>

using namespace std;

typedef long long int ll;
typedef pair<int, int> Pii;

const ll mod = 998244353;

int main() {
  cin.tie(0);
  ios::sync_with_stdio(false);

  int n, m;
  cin >> n >> m;
  vector<vector<int>> edge(n);
  for (int i = 0; i < m; i++) {
    int u, v;
    cin >> u >> v;
    edge[u-1].push_back(v-1);
  }

  int ans = -1;
  vector<vector<bool>> visited(4, vector<bool>(n));
  deque<tuple<int, int, int>> que;
  que.emplace_back(0, 0, 0);
  while (!que.empty()) {
    auto [dist, now_task, now_id] = que.front();
    que.pop_front();
    if (visited[now_task][now_id]) continue;
    visited[now_task][now_id] = true;
    if (now_task == 3 && now_id == 0) {
      ans = dist;
      break;
    }
    if (now_id == n - 2 && (now_task & 1) == 0) {
      que.emplace_front(dist, now_task | 1, now_id);
      continue;
    }
    if (now_id == n - 1 && (now_task & 2) == 0) {
      que.emplace_front(dist, now_task | 2, now_id);
      continue;
    }
    for (auto &next_id: edge[now_id]) {
      if (!visited[now_task][next_id]) {
        que.emplace_back(dist + 1, now_task, next_id);
      }
    }
  }

  cout << ans << endl;

  return 0;
}