#pragma region header
#include <bits/stdc++.h>
#include <atcoder/all>
using namespace std;
using namespace atcoder;

// clang-format off

struct Fast {Fast() {std::cin.tie(0); ios::sync_with_stdio(false);}} fast;

inline void IN(void)
{
    return;
}

template <typename First, typename... Rest>
void IN(First &first, Rest &...rest)
{
    cin >> first;
    IN(rest...);
    return;
}
template <typename T>
istream &operator>>(istream &is, pair<T, T> &p)
{
    is >> p.first >> p.second;
    return is;
}
template <typename T>
istream &operator>>(istream &is, vector<T> &v)
{
    for (auto &x : v)
        is >> x;
    return is;
}
template <typename T>
ostream &operator<<(ostream &os, vector<T> &v)
{
    for (auto &x : v)
        os << x << " ";
    os << endl;
    return os;
}

// templetes
//alias
 
using ull = unsigned long long;
using ll = long long;
using vi = vector<int>;
using vvi = vector<vi>;
using vll = vector<ll>;
using vvll = vector<vll>;
using vb = vector<bool>;
using vvb = vector<vb>;
using vs = vector<string>;
using pll = pair<ll, ll>;
 
//define short
#define vec vector
#define all(obs) (obs).begin(), (obs).end()
#define YESNO(cond) (cond) ? cout << "YES" << endl : cout << "NO" << endl;
#define YesNo(cond) (cond) ? cout << "Yes" << endl : cout << "No" << endl;
#define yesno(cond) (cond) ? cout << "yes" << endl : cout << "no" << endl;
#define sortv(obs) sort(all(obs))
#define rsortv(obs) reverse(sort(all(obs)))
#define bitu(n,i) (((n)>>(i))&1)
#define dig10(n) to_string(n).size()
#define bcnt(n) __builtin_popcount(n)
#define bcntll(n) __builtin_popcountll(n)
#define F first
#define S second
#define pb push_back
#define pq priority_queue


//define loop
#define rep(i, a,b) for(ll i = a; i < (b); i++)
#define rrep(i, a,b) for(ll i = a; i >= (b); i--)
//define INF
const ll INF = 1e18;

template <typename T1,typename T2>
inline void chmin(T1 &a,T2 b){
    if(a>b) a = b;
}
template <typename T1,typename T2>
inline void chmax(T1 &a,T2 b){
    if(a<b) a = b;
}


#pragma endregion header

// clang-format on

int main(){
    ll n,m;
    cin>>n>>m;
    vvll g(n);
    rep(i,0,m){
        ll a,b;
        cin>>a>>b;
        a--;b--;
        g[a].pb(b);
    }
    vll dist0(n,INF),distn(n,INF),distnmi(n,INF);
    dist0[0]=0;
    distn[n-1]=0;
    distnmi[n-2]=0;
    queue<ll> q;
    q.push(0);
    while(!q.empty()){
        ll v=q.front();
        q.pop();
        for(auto nv:g[v]){
            if(dist0[nv]==INF){
                dist0[nv]=dist0[v]+1;
                q.push(nv);
            }
        }
    }
    q.push(n-1);
    while(!q.empty()){
        ll v=q.front();
        q.pop();
        for(auto nv:g[v]){
            if(distn[nv]==INF){
                distn[nv]=distn[v]+1;
                q.push(nv);
            }
        }
    }
    q.push(n-2);
    while(!q.empty()){
        ll v=q.front();
        q.pop();
        for(auto nv:g[v]){
            if(distnmi[nv]==INF){
                distnmi[nv]=distnmi[v]+1;
                q.push(nv);
            }
        }
    }
    ll ans=INF;
    chmin(ans,dist0[n-1]+distn[n-2]+distnmi[0]);
    chmin(ans,dist0[n-2]+distnmi[n-1]+distn[0]);
    if(ans==INF) ans=-1;
    cout<<ans<<endl;
}