// 

#include <bits/stdc++.h>
#include <atcoder/all>
using namespace std;
using namespace atcoder;

using ll = long long;

#define rep(i, n) for (int i=0; i<(int)(n); ++(i))
#define rep3(i, m, n) for (int i=(m); (i)<(int)(n); ++(i))
#define repr(i, n) for (int i=(int)(n)-1; (i)>=0; --(i))
#define rep3r(i, m, n) for (int i=(int)(n)-1; (i)>=(int)(m); --(i))
#define all(x) (x).begin(), (x).end()

const int INF = (int)(1e9);

int main() {
	int n, m;
	cin >> n >> m;
	vector<vector<int>> g(n);
	rep(i, m) {
		int ui, vi;
		cin >> ui >> vi;
		--ui; --vi;
		g[ui].push_back(vi);
	}
	vector<vector<int>> dist(n, vector<int>(4, INF));
	queue<pair<int, int>> que;
	dist[0][0] = 0;
	que.emplace(0, 0);
	while (!que.empty()) {
		auto [vi, si] = que.front(); que.pop();
		int di = dist[vi][si], ndi = di + 1;
		for (const int& ti : g[vi]) {
			int tsi = si | (ti == n-1 ? 1 : ti == n-2 ? 2 : 0);
			if (dist[ti][tsi] <= ndi) continue;
			dist[ti][tsi] = ndi;
			que.emplace(ti, tsi);
		}
	}
	if (dist[0][3] == INF) cout << -1 << endl;
	else cout << dist[0][3] << endl;
	return 0;
}