#include<bits/stdc++.h>
using namespace std;
using ll=long long;

int main(){
  ll n,m;
  cin>>n>>m;
  vector<vector<ll>> G(n);
  for(ll i=0;i<m;i++){
    ll u,v;
    cin>>u>>v;
    u--;
    v--;
    G[u].push_back(v);
  }
  queue<ll> que;
  vector<ll> dist1(n,1e18);
  que.push(0);
  dist1[0]=0;
  while(que.size()){
    ll q=que.front();
    que.pop();
    for(ll u:G[q]){
      if(dist1[u]==1e18){
        dist1[u]=dist1[q]+1;
        que.push(u);
      }
    }
  }
  vector<ll> dist2(n,1e18);
  que.push(n-2);
  dist2[n-2]=0;
  while(que.size()){
    ll q=que.front();
    que.pop();
    for(ll u:G[q]){
      if(dist2[u]==1e18){
        dist2[u]=dist2[q]+1;
        que.push(u);
      }
    }
  }
  vector<ll> dist3(n,1e18);
  que.push(n-1);
  dist3[n-1]=0;
  while(que.size()){
    ll q=que.front();
    que.pop();
    for(ll u:G[q]){
      if(dist3[u]==1e18){
        dist3[u]=dist3[q]+1;
        que.push(u);
      }
    }
  }
  ll ans=1e18;
  ans=min(ans,dist1[n-2]+dist2[n-1]+dist3[0]);
  ans=min(ans,dist1[n-1]+dist3[n-2]+dist2[0]);
  if(ans==1e18){
    cout<<-1<<endl;
  }else{
    cout<<ans<<endl;
  }
}