#include<bits/stdc++.h>
#define MAXN 100010

using namespace std;

vector<int> grafo[MAXN];

queue<int> q;
int marc[MAXN], dist[MAXN], pai[MAXN];
int n;

void bfs(int s){
    q.push(s);
    marc[s] = 1;
    dist[s] = 0;
    pai[s] = -1;
    while(!q.empty()){
        int v = q.front();
        q.pop();
        for(int viz : grafo[v]){
            if(marc[viz] == 0){
                marc[viz] = 1;
                q.push(viz);
                dist[viz] = dist[v]+1;
                pai[viz] = v;
            }
        }
    }
}

int main(){
    int m; scanf("%d %d", &n, &m);

    for(int i = 1; i <= m; i++){
        int a, b; scanf("%d %d", &a, &b);
        grafo[a].push_back(b);
        grafo[b].push_back(a);
    }
    bfs(1);

    if(dist[n] == 0){
        printf("IMPOSSIBLE\n");
        return 0;
    }
    printf("%d\n", dist[n]+1);

    //Encontra o menor caminho da fonte até o vértice v
    vector<int> path;
    path.push_back(n);
    while(pai[n] != -1){
        n = pai[n];
        path.push_back(n);
    }
    //path.push_back(n);

    reverse(path.begin(),path.end());

    for(auto v : path){
        printf("%d ", v);
    }
}