Why my topo code not working!

Hey, I’m trying to learn toposort, It’s not working
I tried to sumbit on this problem

What I tried:
I tried to visualize the graph, and figuring out by myself however I really can’t

here’s my code

#include <bits/stdc++.h>
using namespace std;

const int maxn = 1000001;

int n, m;
vector<int> adj[maxn];
vector<bool> visited;
vector<int> ans;
map<pair<int, int>, bool> ck;

void dfs(int v) {
    visited[v] = true;
    for (int u : adj[v]) {
        if (!visited[u])
            dfs(u);
    }
    ans.push_back(v);
}

void topological_sort() {
    visited.assign(n + 1, false); 
    ans.clear();
    for (int i = 1; i <= n; ++i) {
        if (!visited[i]) {
            dfs(i);
        }
    }
    reverse(ans.begin(), ans.end());
}

int main() {
    cin.tie(0)->sync_with_stdio(0);
    cin >> n >> m;
    
    for (int i = 0; i < m; ++i) {
        int v1, v2;
        cin >> v1 >> v2;
        adj[v1].push_back(v2);
        ck[{v1, v2}] = true;
    }

    for (auto& [key, val] : ck) {
        int v1 = key.first, v2 = key.second;
        if (ck.find({v2, v1}) != ck.end()) {
            cout << "Sandro fails." << '\n';
            return 0;
        }
    }

    topological_sort();

    for (int c : ans) {
        cout << c << " ";
    }

    return 0;
}