#include <bits/stdc++.h>
using namespace std;
#if __has_include(<atcoder/all>)
#include <atcoder/all>
using namespace atcoder;
#endif
using ll = long long;
using ld = long double;
using ull = long long;
#define REP3(i, m, n) for (int i = (m); (i) < int(n); ++ (i))
#define ALL(x) begin(x), end(x)
#define all(s) (s).begin(),(s).end()
#define rep2(i, m, n) for (int i = (m); i < (n); ++i)
#define rep(i, n) rep2(i, 0, n)
#define drep2(i, m, n) for (int i = (m)-1; i >= (n); --i)
#define drep(i, n) drep2(i, n, 0)
#define rever(vec) reverse(vec.begin(), vec.end())
#define sor(vec) sort(vec.begin(), vec.end())
#define fi first
#define se second
#define P pair<ll,ll>
#define REP(i, n) for (int i = 0; i < (n); ++i)
//const ll mod = 998244353;
const ll mod = 1000000007;
const ll inf = 2000000000000000000ll;
static const long double pi = 3.141592653589793;
template<class T>void vcin(vector<T> &n){for(int i=0;i<int(n.size());i++) cin>>n[i];}
template<class T>void vcout(vector<T> &n){for(int i=0;i<int(n.size());i++){cout<<n[i]<<" ";}cout<<endl;}
void YesNo(bool a){if(a){cout<<"Yes"<<endl;}else{cout<<"No"<<endl;}}
void YESNO(bool a){if(a){cout<<"YES"<<endl;}else{cout<<"NO"<<endl;}}
template<class T,class U> void chmax(T& t,const U& u){if(t<u) t=u;}
template<class T,class U> void chmin(T& t,const U& u){if(t>u) t=u;}
template<class T> void ifmin(T t,T u){if(t>u){cout<<-1<<endl;}else{cout<<t<<endl;}}
template<class T> void ifmax(T t,T u){if(t>u){cout<<-1<<endl;}else{cout<<t<<endl;}}
template<typename T,typename ...Args>auto make_vector(T x,int arg,Args ...args){if constexpr(sizeof...(args)==0)return vector<T>(arg,x);else return vector(arg,make_vector<T>(x,args...));}
ll modPow(ll a, ll n, ll mod) { ll ret = 1; ll p = a % mod; while (n) { if (n & 1) ret = ret * p % mod; p = p * p % mod; n >>= 1; } return ret; }

void gbjsmzmfuuvdf(){
  ios::sync_with_stdio(false);
    std::cin.tie(nullptr);
  cout<< fixed << setprecision(20);
}
struct graph{
  struct edge{
    ll to,cost;
  };
  ll v;
  vector<vector<edge>> g;
  vector<ll> d;
  vector<bool> negative;
  vector<bool> diameter;
  vector<ll> topological_sort;
  ll diametercost;
  bool bipartitecheck;
  vector<ll> bipartite;
  graph(ll n){
    init(n);
  }
  void init(ll n){
    v=n;
    g.resize(n);
    d.resize(n);
    negative.resize(n);
    diameter.resize(n);
    bipartite.resize(n);
    for(int i=0;i<v;i++){
      d[i]=inf;
      bipartite[i]=-1;
      negative[i]=false;
      diameter[i]=false;
    }
  }
  void addedge(ll s,ll t,ll cost){
    edge e;
    e.to=t;
    e.cost=cost;
    g[s].push_back(e);
  }
  void dijkstra(ll s){
    for(int i=0;i<v;i++){
      d[i]=inf;
    }
    d[s]=0;
    priority_queue<P,vector<P>,greater<P>> que;
    que.push(P(0,s));
    while(!que.empty()){
      P p=que.top();
      que.pop();
      ll V=p.second;
      if(d[V]<p.first) continue;
      for(auto e:g[V]){
        if(d[e.to]>d[V]+e.cost){
          d[e.to]=d[V]+e.cost;
          que.push(P(d[e.to],e.to));
        }
      }
    }
  }
  void BellmanFord(ll s){
    for(int i=0;i<v;i++){
      d[i]=inf;
      negative[i]=false;
    }
    d[s]=0;
    for(int i=0;i<v;i++){
      for(int V=0;V<v;V++){
        if(d[V]==inf){
          continue;
        }
        for(auto e:g[V]){
          if(d[e.to]>d[V]+e.cost){
            d[e.to]=d[V]+e.cost;
            if(i==v-1){
              negative[e.to]=true;
              negative[V]=true;
            }
          }
        }
      }
    }
  }
  void dfs(ll s){
    for(int i=0;i<v;i++){
      d[i]=inf;
    }
    d[s]=0;
    dfs2(s,-1);
  }
  void dfs2(ll s,ll v){
    for(auto e:g[s]){
      if(e.to==v) continue;
      if(d[e.to]>d[s]+e.cost){
        d[e.to]=d[s]+e.cost;
        dfs2(e.to,s);
      }
    }
  }
  void treediameter(){
    dfs(0);
    ll p=0;
    ll q=0;
    for(int i=0;i<v;i++){
      if(q<d[i]){
        q=d[i];
        p=i;
      }
    }
    diameter[p]=true;
    dfs(p);
    ll p2=0;
    ll q2=0;
    for(int i=0;i<v;i++){
      if(q2<d[i]){
        q2=d[i];
        p2=i;
      }
    }
    diameter[p2]=true;
    diametercost=d[p2];
  }
  void Bipartite(){
    Bipartitedfs(0);
  }
  void Bipartitedfs(ll s,ll cur=0){
    bipartite[s]=cur;
    for(auto e:g[s]){
      if(bipartite[e.to]!=-1){
        if((bipartite[e.to]==bipartite[s])^(!e.cost%2)){
          bipartitecheck=false;
        }
      }
      else{
        if(e.cost%2){
          Bipartitedfs(e.to,1-cur);
        }
        else{
          Bipartitedfs(e.to,cur);
        }
      }
    }
  }
  void topologicalsort(){
    for(int i=0;i<v;i++){
      d[i]=0;
    }
    for(int i=0;i<v;i++){
      if(d[i]) continue;
      topologicaldfs(i);
    }
    rever(topological_sort);
  }
  void topologicaldfs(ll a){
    d[a]=1;
    for(auto e:g[a]){
      if(d[e.to]) continue;
      topologicaldfs(e.to);
    }
    topological_sort.push_back(a);
  }
};
int main() {
  gbjsmzmfuuvdf();
  ll n,m;
  cin>>n>>m;
  graph g(n);
  for(int i=0;i<m;i++){
    ll a,b;
    cin>>a>>b;
    a--;
    b--;
    g.addedge(a,b,1);
    g.addedge(b,a,1);
  }
  g.dijkstra(0);
  ifmax(g.d[n-1],inf/2);
}