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

#define LL long long
#define rep(i, a, b) for(LL i=(a); i<(b); i++)
template <typename T> bool chmin(T& a, const T& b) { return a>b ? a=b,1 : 0; }

int main() {
	int N, M; cin >> N >> M;
	vector<int> E[1<<17];
	rep(_, 0, M) {
		int u, v; cin >> u >> v; u--; v--;
		E[u].push_back(v);
	}
	
	const int inf = 1<<27;
    
    auto bfs = [&](int s) {
    	deque<int> que = {{0, 0}};
    	vector<int> d(N, inf); d[0] = 0;
    	
    	while (!que.empty()) {
    		int i = que.front(); que.pop_front();
    		for(auto j: E[i]) {
    			if (chmin(d[j], d[i]+1)) { que.push_back(j); }
    		}
    	}
    	return d;
    };
    
    auto d0 = bfs(0), d1 = bfs(N-2), d2 = bfs(N-1);
    int ans = inf;
    chmin(ans, d0[N-2] + d1[N-1] + d2[0]);
    chmin(ans, d0[N-1] + d2[N-2] + d1[0]);
    if (ans == inf) { ans = -1; }
    cout << ans;
}