#include<iostream>
#include<vector>
#include<algorithm>

using namespace std;
using ll = long long;

#include<queue>

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

    int n,m;
    cin>>n>>m;
    vector<vector<int>> g(n);
    for(int i = 0;i<m;i++){
        int u,v;
        cin>>u>>v;
        u--;v--;
        g[u].push_back(v);
    }
    vector<vector<int>> ans(n,vector<int>(4,1e9));
    ans[0][0] = 0;
    using dat = pair<int,pair<int,int>>;
    priority_queue<dat,vector<dat>,greater<dat>> que;
    que.push(make_pair(0,make_pair(0,0)));
    while(que.size()){
        int ni = que.top().second.first;
        int t = que.top().second.second;
        if(que.top().first>ans[ni][t]) {
            que.pop();
            continue;
        }
        que.pop();
        for(auto&to:g[ni]){
            int need = ans[ni][t] + 1;
            int nt = t;
            if(to==n-2) nt |= 1;
            if(to==n-1) nt |= 2;
            if(ans[to][nt]<=need) continue;
            ans[to][nt] = need;
            que.push(make_pair(need,make_pair(to,nt)));
        }
    }
    if(ans[0][3]==1e9) ans[0][3] = -1;
    cout<<ans[0][3]<<endl;

}