#include <bits/stdc++.h>
using namespace std;
#define rep(i, n) for (int i = 0; i < (n); ++i)
using ll = long long;
using ull = unsigned long long;

int main() {
  cin.tie(nullptr)->sync_with_stdio(false);
  int n, m;
  cin >> n >> m;
  vector Graph(n, vector<int>());
  rep(_, m) {
    int u, v;
    cin >> u >> v;
    --u, --v;
    Graph[u].push_back(v);
    Graph[v].push_back(u);
  }
  constexpr int INF = 1e9;
  vector<int> dist(n, INF);
  queue<int> q;
  q.push(0);
  dist[0] = 0;
  while (!q.empty()) {
    int v = q.front();
    q.pop();
    for (int u : Graph[v]) {
      if (dist[u] > dist[v] + 1) {
        dist[u] = dist[v] + 1;
        q.push(u);
      }
    }
  }
  cout << (dist[n - 1] == INF ? -1 : dist[n - 1]) << '\n';
  return 0;
}