// compile: g++ -o data data.cpp -std=gnu++20 -DLOCAL -g
// run: ./data < data.in
#include <bits/stdc++.h>
#pragma GCC optimize("O3,unroll-loops")
#pragma GCC target("avx2,bmi,bmi2,lzcnt,popcnt")
#ifdef LOCAL
#endif
#define sz(v) ((int)(v).size())
#define PV(v) for (int i=0;i<v.size();++i)cout<<v[i]<<" ";cout<<endl;
#define OK cout<<"OK"<<endl;
#define INTINF 9223372036854775807
#define int long long
#define MAXN 100010

using namespace std;

int n, m;
int s, d;
vector<int> e[MAXN];
int pre[MAXN];
vector<int> q;

int bfs() {
    vector<bool> vis(n + 1, 0);
    q.push_back(s); vis[s] = 1;
    int head = 0, tail = 0;
    while (head <= tail) {
        int u = q[head++];
        for (int v: e[u]) {
            if (vis[v]) continue;
            q.push_back(v); vis[v] = 1; ++tail;
            pre[v] = u;
            if (v == d) return d;
        }
    }
    return -1;
}

void output(int lst) {
    vector<int> a; a.clear();
    for (int x = lst; x; x = pre[x]) {
        a.push_back(x);
    }
    reverse(a.begin(), a.end());
    cout << sz(a) << endl;
    PV(a);
}

int32_t main() {
    ios::sync_with_stdio(false); cin.tie(nullptr); cout.tie(nullptr);

    cin >> n >> m;
    for (int i = 0; i < m; ++i) {
        int u, v; cin >> u >> v;
        e[u].push_back(v);
        e[v].push_back(u);
    }
    s = 1; d = n;
    memset(pre, 0, sizeof(pre));
    int lst = bfs();
    if (!~lst) {
        cout << "IMPOSSIBLE\n";
    }
    else {
        output(lst);
    }

    return 0;
}