#include<iostream>
#include<vector>
#include<algorithm>
#include<cstring>
#include<cassert>
#include<cmath>
#include<ctime>
#include<iomanip>
#include<numeric>
#include<stack>
#include<queue>
#include<map>
#include<unordered_map>
#include<set>
#include<unordered_set>
#include<bitset>
#include<random>
#include<functional>
#include<utility>
using namespace std;
int N,M;
vector<int> G[1 << 17];
int dp[1 << 17][1 << 2];
void solve()
{
	cin >> N >> M;
	for(int i = 0;i < M;i++)
	{
		int u,v;
		cin >> u >> v;
		u--; v--;
		G[u].push_back(v);
	}
	for(int i = 0;i < N;i++)for(int j = 0;j < 1 << 2;j++) dp[i][j] = -1;
	dp[0][0] = 0;
	queue<pair<int,int>> Q;
	Q.push(make_pair(0,0));
	while(!Q.empty())
	{
		auto [u,s] = Q.front();
		Q.pop();

		for(int v:G[u])
		{
			int ns = s;
			if(v == N-2) ns |= 1 << 0;
			if(v == N-1) ns |= 1 << 1;
			if(dp[v][ns] < 0) 
			{
				dp[v][ns] = dp[u][s] + 1;
				Q.push(make_pair(v,ns));
			}
		}
	}
	cout << dp[0][3] << endl;
}
int main()
{
	ios::sync_with_stdio(false);
	cin.tie(nullptr);
	int tt = 1;
	/* cin >> tt; */
	while(tt--) solve();
}