#include <bits/stdc++.h>

using namespace std;

const int INF = 1 << 25;

void bfs(vector<vector<int>>& G, vector<int>& dis, int s) {
    dis[s] = 0;
    queue<int> q;
    q.push(s);
    while (!q.empty()) {
        int v = q.front();
        q.pop();
        for (int nv: G[v]) {
            if (dis[nv] == INF) {
                dis[nv] = dis[v] + 1;
                q.push(nv);
            }
        }
    }
}

int main() {
    int N, M;
    cin >> N >> M;
    vector<vector<int>> G(N);
    for (int i = 0; i < M; i++) {
        int u, v;
        cin >> u >> v;
        u--, v--;
        G[u].push_back(v);
    }
    vector<int> dis0(N, INF), dis1(N, INF), dis2(N, INF);
    bfs(G, dis0, 0);
    bfs(G, dis1, N - 2);
    bfs(G, dis2, N - 1);
    int ans = min(dis0[N - 2] + dis1[N - 1] + dis2[0], dis0[N - 1] + dis2[N - 2] + dis1[0]);
    if (ans >= INF) {
        cout << -1 << endl;
    } else {
        cout << ans << endl;
    }
    return 0;
}