#include <bits/stdc++.h>
using namespace std;
#define rep(i,n) for (int i = 0; i < (n); i++)
template<typename T> inline bool chmax(T &a, T b) {return ((a < b) ? (a = b, true) : (false));}
template<typename T> inline bool chmin(T &a, T b) {return ((a > b) ? (a = b, true) : (false));}
typedef long long ll;
typedef pair<ll,ll> P;

struct edge { 
    ll to, cost; 
    edge(ll to, ll cost): to(to), cost(cost) {}
};
ll MAX_V = 200005, INF = 1001001001001001;
vector<vector<edge>> G(MAX_V);
vector<ll> d(MAX_V,INF);

void dijkstra(int s) {
    priority_queue<P,vector<P>,greater<P>> que;
    d[s] = 0;
    que.emplace(0, s);
    
    while(!que.empty()) {
        P p = que.top(); que.pop();
        int v = p.second;
        if(d[v] < p.first)
            continue;
        rep(i,G[v].size()) {
            edge e = G[v][i];
            if(d[e.to] > d[v] + e.cost) {
                d[e.to] = d[v] + e.cost;
                que.emplace(d[e.to], e.to);
            }
        }
    }
}

int main() {
    ll n, m;
    cin >> n >> m;
    vector<ll> u(m), v(m);
    rep(i,m) cin >> u[i] >> v[i];

    rep(i,m) {
        G[u[i]].emplace_back(v[i],1);
    }

    ll sum1 = 0, sum2 = 0;
    dijkstra(1);
    sum1 += d[n-1];
    sum2 += d[n];
    rep(i,MAX_V) {
        d[i] = INF;
    }
    //cout << " " << sum1 << " " << sum2 << endl;
    dijkstra(n-1);
    sum1 += d[n];
    sum2 += d[1];
    rep(i,MAX_V) {
        d[i] = INF;
    }
    //cout << " " << sum1 << " " << sum2 << endl;
    dijkstra(n);
    sum1 += d[1];
    sum2 += d[n-1];

    ll ans = min(sum1, sum2);
    if(ans >= INF)
        ans = -1;
    cout << ans << endl;







    return 0;
}