#include <bits/stdc++.h>
using namespace std;
using ll = long long;
#define rep(i, s, e) for (int i = (int)(s); i < (int)(e); ++i)
#define all(a) (a).begin(),(a).end()

int INF = 1 << 25;

vector<int> bfs(int s, int N, vector<vector<int>> &G) {
    queue<int> que;
    vector<int> res(N, INF);
    que.push(s);
    res[s] = 0;
    
    while (!que.empty()) {
        int v = que.front();
        que.pop();
        for (int next : G[v]) {
            if (res[next] != INF) continue;
            res[next] = res[v] + 1;
            que.push(next);
        }
    }
    
    return res;
}

int main() {
    cin.tie(nullptr);
    ios_base::sync_with_stdio(false);
    
    int N, M;
    cin >> N >> M;
    vector<vector<int>> G(N);
    rep(i, 0, M) {
        int u, v;
        cin >> u >> v;
        G[u - 1].push_back(v - 1);
    }
    
    vector<int> d1 = bfs(0, N, G);
    vector<int> d2 = bfs(N - 2, N, G);
    vector<int> d3 = bfs(N - 1, N, G);
    
    int ans1 = d1[N - 2] + d2[N - 1] + d3[0];
    int ans2 = d1[N - 1] + d3[N - 2] + d2[0];
    
    if (min(ans1, ans2) >= INF) cout << -1 << '\n';
    else cout << min(ans1, ans2) << '\n';
}