int n;
int graph[10000][10000];

void dfs(int start) {
    stack<pair<int, int>> st;
    vector<int> used(n);

    st.push(make_pair(start, 0));
    used[start] = 1;

    while (!st.empty()) {
        if (st.top().second == 0) {
            cout << st.top().first << endl;
        }

        for (pair<int, int> & cur = st.top(); cur.second < n; ++cur.second) {
            if (graph[cur.first][cur.second] && !used[cur.second]) {
                st.push(make_pair(cur.second, 0));
                used[cur.second] = 1;
                break;
            }
        }

        if (st.top().second == n) {
            st.pop();
        }
    }
}