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

int main(){
    ios_base::sync_with_stdio(false);
    cin.tie(nullptr);

    int N,M; cin >> N >> M;
    vector<vector<pair<int,int>>> Graph(4*N);
    for(int i=0; i<M; i++){
        int u,v; cin >> u >> v;
        u--; v--;
        for(int k=0; k<4; k++){
            Graph.at(u).push_back({v,1});
            u += N, v += N;
        }
    }

    Graph.at(N-2).push_back({N-2+N,0});
    Graph.at(N-2+2*N).push_back({N-2+3*N,0});
    Graph.at(N-1).push_back({N-1+2*N,0});
    Graph.at(N-1+N).push_back({N-1+3*N,0});

    vector<bool> already(4*N);
    vector<long long> dist(4*N,2e18);
    priority_queue<pair<long long,int>,vector<pair<long long,int>>,greater<pair<long long,int>>> Q;
    Q.push({0,0}); dist.at(0) = 0;
    while(Q.size()){
        auto[pdist,pos] = Q.top(); Q.pop();
        if(already.at(pos)) continue;
        already.at(pos) = true;
        
        for(auto [to,cost] : Graph.at(pos)){
            if(dist.at(to) > pdist+cost){
                dist.at(to) = pdist+cost;
                Q.push({dist.at(to),to});
            }
        }
    }

    if(dist.at(3*N) == 2e18) dist.at(3*N) = -1;
    cout << dist.at(3*N) << endl;
}