#include <bits/stdc++.h>
using namespace std;
#include <atcoder/all>
using namespace atcoder;
#define rep(i, n) for(int i=0;i<(n);++i)
#define rep1(i, n) for(int i=1;i<=(n);i++)
#define ll long long
using mint = modint998244353;
using P = pair<ll,ll>;
using lb = long double;
using T = tuple<ll, ll, ll>;
#ifdef LOCAL
#  include <debug_print.hpp>
#  define dbg(...) debug_print::multi_print(#__VA_ARGS__, __VA_ARGS__)
#else
#  define dbg(...) (static_cast<void>(0))
#endif

int main()
{
    int n, m;
    cin >> n >> m;
    vector<vector<int>> g(n);
    rep(i,m){
        int a, b;
        cin >> a >> b;
        --a;--b;
        g[a].push_back(b);
    }
    const int INF = 1e9;
    vector<int> dist(n, INF), dist1(n, INF), dist2(n, INF);
    queue<int> q;
    dist[0] = 0;
    q.push(0);
    while(!q.empty()){
        int u = q.front();q.pop();
        for(int v : g[u]){
            if(dist[v]==INF) {
                dist[v] = dist[u] + 1;
                q.push(v);
            }
        }
    }
    dist1[n-2] = 0;
    q.push(n-2);
    while(!q.empty()){
        int u = q.front();q.pop();
        for(int v : g[u]){
            if(dist1[v]==INF) {
                dist1[v] = dist1[u] + 1;
                q.push(v);
            }
        }
    }
    dist2[n-1] = 0;
    q.push(n-1);
    while(!q.empty()){
        int u = q.front();q.pop();
        for(int v : g[u]){
            if(dist2[v]==INF) {
                dist2[v] = dist2[u] + 1;
                q.push(v);
            }
        }
    }
    int ans = INF;
    dbg(dist);
    dbg(dist1);
    dbg(dist2);
    ans = min(ans, dist[n-2] + dist1[n-1] + dist2[0]);
    ans = min(ans, dist[n-1] + dist2[n-2] + dist1[0]);
    if(ans==INF) ans = -1;
    cout << ans << endl;
    return 0;
}