Shared code

//PPAP_1264589
#include <bits/stdc++.h>
#define Task "A"
#define up(i,a,b) for (int i = a; i <= b; i++)
#define down(i,a,b) for (int i = a; i >= b; i--)
#define pii pair<int, int>
#define f first
#define s second
#define ep emplace_back
#define bit(x,i) ((x >> i) & 1)
using namespace std;
const int LIM = 1010580540;
const int MOD = 1e9 + 7;
 
const int maxn = 1e5 + 10;
int dp[maxn];
int check[maxn];
int tr[maxn];
vector<int> a[maxn];
int n,m;
 
void in(){
    cin >> n >> m;
    up(i,1,m){
        int u,v;
        cin >> u >> v;
        if (check[u] == v) continue;
        check[u] = v;
        a[u].ep(v);
    }
}
 
void DFS(int u){
    for (int v : a[u]){
        DFS(v);
        if (dp[v]){
            if (dp[u] < dp[v] + 1){
                dp[u] = dp[v] + 1;
                tr[u] = v;
            }
        }
    }
}
 
void Fpath(){
    int x = 1;
    vector<int> path;
    while (x != n){
        path.ep(x);
        x = tr[x];
    }
    path.ep(n);
    for (auto x : path) cout << x << " ";
}
 
signed main(){
    ios_base::sync_with_stdio(false);
    cin.tie(0);
    if (fopen(Task".inp", "r")){
        freopen (Task".inp", "r", stdin);
        freopen (Task".out", "w", stdout);
    }
 
    in();
    dp[n] = 1;
    DFS(1);
    if (dp[1] == 0) cout << "IMPOSSIBLE";
    else {
        cout << dp[1] << "\n";
        Fpath();
    }
 
}
 
// Algorithmic logic