#include <bits/stdc++.h>
using namespace std;
using ll = long long;
const int INF = 1 << 30;

bool chmin(int& a, int b) {
    if(a > b) {
        a = b;
        return true;
    }
    return false;
}

#define REP(i, n) for(int i=0;i<(int)(n);i++)

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);
        G[b].push_back(a);
    }
    vector<int> dp(N, INF);
    dp[0] = 0;
    queue<int> que;
    que.push(0);
    while(!que.empty()) {
        int u = que.front(); que.pop();
        for(int v : G[u]) {
            if(chmin(dp[v], dp[u] + 1)) que.push(v);
        }
    }
    int ans = dp[N-1];
    if(ans == INF) ans = -1;
    cout << ans << endl;
}