#include <bits/stdc++.h>
using namespace std;
const int MAX_N = 100'009;
int N;
int visited[MAX_N];

void v_clear()
{
    for (int i = 0; i < N; i++)
        visited[i] = -1;
}

void bfs(vector<vector<int>> &Graph, queue<int> &Q, int first)
{
    v_clear();
    visited[first] = 0;
    Q.push(first);
    while (!Q.empty())
    {
        int place = Q.front();
        Q.pop();
        for (int next : Graph[place])
        {
            if (visited[next] != -1)
                continue;
            visited[next] = visited[place] + 1;
            Q.push(next);
        }
    }
}

int main()
{
    int M;
    cin >> N >> M;
    vector<vector<int>> Graph(N, vector<int>(0));
    for (int i = 0; i < M; i++)
    {
        int u, v;
        cin >> u >> v;
        u--, v--;
        Graph[u].push_back(v);
    }
    queue<int> Q;
    int len1toN, len1toN_bfr, lenN_bfrto1, lenN_bfrtoN, lenNto1, lenNtoN_bfr;
    // 1 -> N-1, 1 -> N
    bfs(Graph, Q, 0);
    len1toN = visited[N - 1];
    len1toN_bfr = visited[N - 2];
    // N-1 -> 1, N-1 -> N
    bfs(Graph, Q, N - 2);
    lenN_bfrto1 = visited[0];
    lenN_bfrtoN = visited[N-1];
    // N -> 1, N -> N-1
    bfs(Graph, Q, N - 1);
    lenNto1 = visited[0];
    lenNtoN_bfr = visited[N - 2];

    // cout << len1toN << endl;
    // cout << len1toN_bfr << endl;
    // cout << lenN_bfrto1 << endl;
    // cout << lenN_bfrtoN << endl;
    // cout << lenNto1 << endl;
    // cout << lenNtoN_bfr << endl;

    int path1, path2;
    if (len1toN_bfr == -1 || lenN_bfrtoN == -1 || lenNto1 == -1)
        path1 = -1;
    else
        path1 = len1toN_bfr + lenN_bfrtoN + lenNto1;
    if (len1toN == -1 || lenNtoN_bfr == -1 || lenN_bfrto1 == -1)
        path2 = -1;
    else
        path2 = len1toN + lenNtoN_bfr + lenN_bfrto1;
    if (path1 == -1 && path2 == -1)
        cout << -1 << endl;
    else if (path1 == -1)
        cout << path2 << endl;
    else if (path2 == -1)
        cout << path1 << endl;
    else
        cout << min(path1, path2) << endl;
}