#define _USE_MATH_DEFINES
#include <iostream>
#include <string>
#include <algorithm>
#include <vector>
#include <queue>
#include <math.h>
#include <cmath>
#include <stack>
#include <map>
#include <set>
#include <numeric>
#include <iomanip>
#include <climits>
#include <functional>
#include <cassert>
#include <tuple>
using namespace std;
using ll = long long;

int N, M;
vector<int> G[101010];

void wfs(int t, vector<int> &vis) {

    vis[t] = 0;
    queue<int> q;
    q.push(t);

    while(!q.empty()) {
        int v = q.front();
        q.pop();
        for(int ne : G[v]) {
            if(vis[ne] != -1) continue;
            vis[ne] = vis[v]+1;
            q.push(ne);
        }
    }

}

int main() {
    
    cin >> N >> M;
    for(int i = 0; i < M; ++i) {
        int u,v; cin >> u >> v;
        G[u].push_back(v);
    }

    vector<int> vis1(N+1, -1);
    vector<int> visN_1(N+1, -1);
    vector<int> visN(N+1, -1);

    wfs(1,vis1);
    wfs(N-1,visN_1);
    wfs(N,visN);

    int mn = 1e9;
    if(vis1[N-1] != -1 
    && visN_1[N] != -1 
    && visN[1] != -1) mn = min(mn, vis1[N-1]+visN_1[N]+visN[1]);

    
    if(vis1[N] != -1 
    && visN[N-1] != -1 
    && visN_1[1] != -1) mn = min(mn, vis1[N]+visN[N-1]+visN_1[1]);

    cout << (mn != 1e9 ? mn : -1) << endl;

}