#include <bits/stdc++.h>

using namespace std;
typedef long long ll;
typedef pair<ll, ll> p_ll;

template<class T>
void debug(T itr1, T itr2) { auto now = itr1; while(now<itr2) { cout << *now << " "; now++; } cout << endl; }
#define repr(i,from,to) for (ll i=(ll)from; i<(ll)to; i++)
#define all(vec) vec.begin(), vec.end()
#define rep(i,N) repr(i,0,N)
#define per(i,N) for (ll i=(ll)N-1; i>=0; i--)
#define popcount __builtin_popcount

const ll LLINF = pow(2,61)-1;
const ll INF = pow(2,30)-1;

ll gcd(ll a, ll b) { if (a<b) swap(a,b); return b==0 ? a : gcd(b, a%b); }
ll lcm(ll a, ll b) { return a/gcd(a,b)*b; }

int main() {
  ll N, M; cin >> N >> M;
  ll a[M], b[M]; rep(i,M) { cin >> a[i] >> b[i]; a[i]--; b[i]--; }
  vector<vector<ll>> adj(N);
  rep(i,M) {
    adj[a[i]].push_back(b[i]);
    adj[b[i]].push_back(a[i]);
  }
  vector<ll> d(N,-1); d[0] = 0;
  queue<ll> q; q.push(0);
  while (q.size()) {
    ll now = q.front(); q.pop();
    for (auto x: adj[now]) {
      if (d[x]!=-1) continue;
      d[x] = d[now]+1;
      q.push(x);
    }
  }
  ll result = d[N-1];
  cout << result << endl;
  return 0;
}