#include <algorithm>
#include <array>
#include <bitset>
#include <cassert>
#include <chrono>
#include <cmath>
#include <complex>
#include <cstdint>
#include <cstring>
#include <ctime>
#include <deque>
#include <iomanip>
#include <iostream>
#include <iterator>
#include <map>
#include <numeric>
#include <queue>
#include <random>
#include <set>
#include <stack>
#include <unordered_map>
#include <unordered_set>

void solve() {
  int n, m;
  std::cin >> n >> m;
  std::vector<std::vector<int>> g(n);

  for (int i = 0; i < m; i++) {
    int u, v;
    std::cin >> u >> v;
    u--, v--;
    g[u].push_back(v);
  }
  std::vector dp(n, std::vector<int>(4, 1e8));
  std::queue<std::pair<int, int>> q;  // 11
  q.emplace(0, 0);                    // final state (0, 11);
  dp[0][0] = 0;
  while (!q.empty()) {
    auto [u, state] = q.front();
    q.pop();

    for (int v : g[u]) {
      int nxt = state;
      if (v == n - 2) {
        nxt = (state | 2);
      }
      if (v == n - 1) {
        nxt = (state | 1);
      }
      if (dp[v][nxt] == 1e8) {
        dp[v][nxt] = dp[u][state] + 1;

        q.emplace(v, nxt);
      }
    }
  }
  if (dp[0][3] == 1e8) dp[0][3] = -1;
  std::cout << dp[0][3] << '\n';
}
int main() {
  std::ios_base::sync_with_stdio(false);
  std::cin.tie(nullptr);

  int t = 1;
  // std::cin >> t;
  while (t--) {
    solve();
  }
}