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

int main() {
    int N,M;
    cin >> N >> M;
    vector<vector<int>>road(N);
    for(int i = 0; i < M; i++) {
        int a,b;
        cin >> a >> b;
        a--;
        b--;
        road[a].push_back(b);
        road[b].push_back(a);
    }
    vector<int>dist(N,-1);
    dist[0] = 0;
    queue<int>que;
    que.push(0);
    while (!que.empty()) {
        int x = que.front();
        que.pop();
        for(int i = 0; i < road[x].size(); i++) {
            if(dist[road[x][i]] == -1) {
                dist[road[x][i]] = dist[x]+1;
                que.push(road[x][i]);
            }
        }
    }
    cout << dist[N-1] << endl;
}