#include <bits/stdc++.h>
using namespace std;
int main(){
	int N, M;
	cin >> N >> M;
	vector<vector<long long>> G(N);
	for (int i = 0; i < M; i++){
		int u, v;
		cin >> u >> v;
		u--;
		v--;
		G[u].push_back(v);
	}
	long long ans = 1e18;
	vector<vector<long long>> D;
	for (int i : {0, N - 2, N - 1}){
		queue<int> q;
		vector<long long> d(N, 1e18);
		q.push(i);
		d[i] = 0;
		while (!q.empty()){
			int v = q.front();
			q.pop();
			for (int i : G[v]){
				if (d[i] == 1e18){
					d[i] = d[v] + 1;
					q.push(i);
				}
			}
		}
		D.push_back(d);
	}
	ans = min(ans, D[0][N - 2] + D[1][N - 1] + D[2][0]);
	ans = min(ans, D[0][N - 1] + D[2][N - 2] + D[1][0]);
	if (ans != 1e18){
		cout << ans << endl;
	} else {
		cout << -1 << endl;
	}
}