#include <iostream>
#include <vector>
#include <queue>

using namespace std;

int main()
{
	cin.tie(nullptr);
	ios::sync_with_stdio(false);

	int N, M, u, v, i;
	cin >> N >> M;
	vector<vector<int>> edges(N, vector<int>());
	for (i = 0; i != M; ++i) cin >> u >> v, edges[u - 1].push_back(v - 1);

	vector<vector<int>> dist(4, vector<int>(N, -1));
	queue<pair<int, int>> q;
	q.emplace(0, 0), dist[0][0] = 0;
	while (!q.empty())
	{
		for (i = 0; i != edges[q.front().second].size(); ++i)
		{
			if (dist[q.front().first][edges[q.front().second][i]] == -1)
				q.emplace(q.front().first, edges[q.front().second][i]), dist[q.front().first][edges[q.front().second][i]] = dist[q.front().first][q.front().second] + 1;

			if (edges[q.front().second][i] == N - 1 && dist[q.front().first | 1][edges[q.front().second][i]] == -1)
				q.emplace(q.front().first | 1, edges[q.front().second][i]), dist[q.front().first | 1][edges[q.front().second][i]] = dist[q.front().first][q.front().second] + 1;
			if (edges[q.front().second][i] == N - 2 && dist[q.front().first | 2][edges[q.front().second][i]] == -1)
				q.emplace(q.front().first | 2, edges[q.front().second][i]), dist[q.front().first | 2][edges[q.front().second][i]] = dist[q.front().first][q.front().second] + 1;
		}

		q.pop();
	}

	cout << dist[3][0] << '\n';
	return 0;
}