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input/code.cpp: In function 'int main()':
input/code.cpp:49:19: warning: unused variable 'w' [-Wunused-variable]
   49 |         int u, v, w;
      |                   ^

#include <bits/stdc++.h>
using namespace std;
#define sz(x) (int)(x).size()
#define all(x) (x).begin(), (x).end()
#define int long long
 
const int N = 1e5 + 5;
const int M = 2e5 + 5;
 
int n, m;
vector<int> adj[N];
 
bool vis[N];
list<int> lst;
 
void dfs(int u) {
    for (int v : adj[u]) {
        if (!vis[v]) {
            vis[v] = 1;
            dfs(v);
        }
    }
    lst.push_front(u);
}
 
int tin[N];
bool check() {
    int timer = 1;
    for (int x : lst) {
        tin[x] = timer++;
    }
 
    for (int u = 1; u <= n; u++) {
        for (int v : adj[u]) {
            if (tin[v] <= tin[u]) {
                return false;
            }
        }
    }
 
    return true;
}
 
signed main() {
    cin.tie(0)->sync_with_stdio(0);
    
    cin >> n >> m;
    for (int i = 1; i <= m; i++) {
        int u, v, w;
        cin >> u >> v;
        adj[u].push_back(v);
    }        
 
    for (int i = 1; i <= n; i++) {
        if (!vis[i]) {
            vis[i] = 1;
            dfs(i);
        }
    }
 
    if (check()) {
        for (int x : lst) cout << x << ' ';
        cout << '\n';
    } else {
        cout << "IMPOSSIBLE\n";
    }
}

Test 1

Verdict: ACCEPTED

Test 2

Verdict: ACCEPTED

Test 3

Verdict: ACCEPTED

Test 4

Verdict: ACCEPTED

Test 5

Verdict: ACCEPTED

Test 6

Verdict: ACCEPTED

Test 7

Verdict: ACCEPTED

Test 8

Verdict: ACCEPTED

Test 9

Verdict: ACCEPTED

Test 10

Verdict: ACCEPTED

Test 11

Verdict: ACCEPTED

Test 12

Verdict: ACCEPTED

Test 13

Verdict: ACCEPTED

Test 14

Verdict: ACCEPTED

Test 15

Verdict: ACCEPTED

Test 16

Verdict: ACCEPTED

Test 17

Verdict: ACCEPTED