#include <bits/stdc++.h>
using namespace std;
using ll = long long;
using P = pair<ll, ll>;
using T = tuple<ll, ll, ll>;
// #include <atcoder/all>
// using namespace atcoder;
// using mint = modint1000000007;
#define rep(i, n) for(ll i = 0; i < n; i++)

int main() {
    cin.tie(nullptr);
    ios_base::sync_with_stdio(false);
    
    ll n, m; cin >> n >> m;
    vector<vector<ll>> Graph(4*n);
    vector<ll> vis(4*n,-1);
    rep(i,m) {
        ll u, v; cin >> u >> v; u--; v--;
        Graph[u].emplace_back(v);
        Graph[n+u].emplace_back(n+v);
        Graph[2*n+u].emplace_back(2*n+v);
        Graph[3*n+u].emplace_back(3*n+v);
    }
    Graph[n-2].emplace_back(n+(n-2));
    Graph[n-1].emplace_back(2*n+(n-1));
    Graph[n+(n-1)].emplace_back(3*n+(n-1));
    Graph[2*n+(n-2)].emplace_back(3*n+(n-2));

    queue<P> todo;
    todo.push(P(0,0));
    while( !todo.empty() ) {
        auto [idx,dis] = todo.front(); todo.pop();
        if( vis[idx] != -1 ) continue;
        vis[idx] = dis;
        for(auto to:Graph[idx]) {
            if( vis[to] != -1 ) continue;
            todo.push(P(to,dis+1));
        }
    }
    cout << (vis[3*n] == -1 ? -1 : vis[3*n]-2) << endl;
    
    return 0;
}