Shared code

#include <iostream>
#include <vector>
#include <queue>
#include <stack>
#include <map>
#include <set>
#include <string>
#include <algorithm>
#include <string>
#include <cmath>
#include <numeric>
#include <unordered_set>


using namespace std;
//Macros
#define  ll      long long int
#define  endl    "\n"
#define  fastIO  ios_base::sync_with_stdio(false);cin.tie(NULL);
#define  pb push_back
#define pll pair<ll,ll>
#define F first
#define S second
#define  ml map<ll,ll>
#define  vl vector<ll>
#define vs <vector <string>>
#define vvl vector <vector<ll>>
#define vpl vector <pair<ll,ll>>
#define vlvlpl vector <vector<pair<ll,ll>>>
#define pl pair<ll,ll>
#define  isTestCases 0
#define  showTime 0


const ll nodes = 2e5 + 10;
vl adj[nodes];
vector <ll> parent(nodes,-1);
vector <ll> inNodes(nodes);
vector <ll> dep(nodes);

ll n,m;
void  addEdges(ll &m ){
    for(ll i = 0;i<m;i++) {
        ll x,y;
        cin>>x>>y;
        adj[x].push_back(y);
        inNodes[y]++;

    }
}


struct cmp
{
    bool operator() (const pl &a, const pl &b)const{
        return (a.S>b.S);
    }
};


void traverse(){

    ll curnd = n;
    vector <ll> ans;
    while(parent[curnd]!=-1){
        ans.push_back(curnd);
        curnd = parent[curnd];
    }
    ans.push_back(1);
    cout<<ans.size()<<endl;
    for(ll i = ans.size()-1;i>=0;i--)cout<<ans[i]<<' ';
}


void topsort(queue <ll> &que){
    while (!que.empty()) {
        ll node = que.front();
        que.pop();
        // Enqueue all adjacent of f and mark them visited
        for(ll x:adj[node]){
            inNodes[x]--;
            if(inNodes[x] == 0){
                parent[x] = node;
                que.push(x);
            }
        }
    }
}




void solve(){
    cin>>n>>m;
    vl cst (n+1);
    for(ll i=2;i<=n;i++){
        cst[i] = INT64_MAX;
    }
    cst[0]=0;
    addEdges(m);


    queue <ll> que;
    vector <ll> ans;
    for(ll i =2;i<=n;i++){
        if(inNodes[i]==0 )que.push(i);
    }

    topsort(que);
    que.push(1);
    parent[n]=-1;
    topsort(que);


    if(parent[n] ==-1)
        cout<<"IMPOSSIBLE"<<endl;
        else traverse();
}




int main(){
    fastIO
    ll t=1;
#if isTestCases
    cin>>t;
#endif
    while(t--){
        solve();
    }
    return 0;
}