#define _USE_MATH_DEFINES
#include  <cmath>
#include <cstdio>
#include <vector>
#include <iostream>
#include <algorithm>
#include <string>
#include<math.h>
#include<iomanip>
#include<stdio.h>
#include <stdlib.h>
#include<stdio.h>
#include <queue>
#include<map>
#include <fstream>
#include <sstream>
#include<set>
#include<stack>
#include<time.h>
#include <sys/types.h>
#include <tuple>
#include <numeric>
#include <iterator>

typedef long long int ll;
//#include<bits/stdc++.h>


using namespace std;

ll gcd(ll a, ll b) {
    if (a < b)swap(a, b);
    if (b == 0)return a;
    return gcd(b, a % b);
}
int lcm(int a, int b) {
    return a * b / gcd(a, b);
}




int main()
{

    int Q;
    Q = 1;
    //cin >> Q;



    while (Q--) {
        int n, m;
        cin >> n >> m;
        vector<vector<int>>r(n+1);
        for (int i = 0; i < m; i++) {
            int a, b;
            cin >> a >> b;
            a--; b--;
            r[a].push_back(b);
        }
        vector<ll>x(n + 1,1e9);
        
        queue<int>q;
        x[0] = 0;
        q.push(0);
        int now = 0;
        while (q.size()) {
            int to = q.front();
            for (int i = 0; i < r[to].size(); i++) {
                if (x[r[to][i]] == 1e9) {
                    x[r[to][i]] = x[to] + 1;
                    q.push(r[to][i]);
                    //cout << to << " " << r[to][i] << endl;
                }
            }
            q.pop();
        }

        vector<ll>x1(n + 1, 1e9);
        queue<int>q1;
        x1[n-2] = 0;
        q1.push(n-2);

        while (q1.size()) {
            int to = q1.front();
            for (int i = 0; i < r[to].size(); i++) {
                if (x1[r[to][i]] == 1e9) {
                    x1[r[to][i]] = x1[to] + 1;
                    q1.push(r[to][i]);
                }
            }
            q1.pop();
        }
        vector<ll>x2(n + 1, 1e9);
        queue<int>q2;
        x2[n - 1] = 0;
        q2.push(n - 1);

        while (q2.size()) {
            int to = q2.front();
            for (int i = 0; i < r[to].size(); i++) {
                if (x2[r[to][i]] == 1e9) {
                    x2[r[to][i]] = x2[to] + 1;
                    q2.push(r[to][i]);
                }
            }
            q2.pop();
        }
        //cout << x[n - 2];
        ll ans = min(x[n - 2] + x1[n - 1] + x2[0], x[n - 1] + x2[n - 2] + x1[0]);
        if (ans > 1e9)ans = -1;
        cout << ans;
    }
        return 0;
}